WBCS Main Chemistry Questions and Answers (Previous Year Paper)

Answer: (C) 5

Explanation: Degrees of freedom are the independent ways a molecule can store energy. H₂ is a diatomic, linear molecule. It has 3 translational degrees of freedom, for motion along the x, y and z axes. It has 2 rotational degrees of freedom, because rotation about the bond axis is negligible for a linear molecule and only the two rotations perpendicular to the axis count. This gives 3 + 2 = 5. The vibrational modes (2 more, one kinetic and one potential) are not excited at ordinary temperatures, so they are not counted. They become active only at very high temperatures, when the total rises to 7.

Degrees of Freedom:

Answer: (D) Epidiolex

Explanation: The world’s first medicine derived from marijuana (cannabis) to receive regulatory approval is Epidiolex, an oral solution containing purified cannabidiol (CBD). It was approved by the US FDA in June 2018 for treating seizures associated with two severe, rare forms of epilepsy, Lennox-Gastaut syndrome and Dravet syndrome, and later for seizures linked to tuberous sclerosis complex. CBD is the non-intoxicating component of cannabis, so the drug does not produce a “high” the way THC does. The option is spelled “Epidolex” in the paper, but it refers to Epidiolex.

Cannabis-Derived and Related Medicines:

Answer: (C) Isobutane

Explanation: HFCs such as R-134a were used in refrigerators after CFCs and HCFCs were phased out for damaging the ozone layer. HFCs do not harm ozone, but they have a very high global warming potential (R-134a is about 1430 times CO₂). Domestic refrigerators have therefore been moving to isobutane (R-600a), a hydrocarbon refrigerant. It has zero ozone depletion potential and a global warming potential of about 3, and it is energy efficient. It is flammable, so only small charges are used in sealed household units.

Answer: (D) Fatty acid and glycerol

Explanation: A triglyceride is an ester formed from one glycerol molecule joined to three fatty acid chains. During digestion, the enzyme lipase hydrolyses the ester bonds. In the small intestine, pancreatic lipase, helped by bile salts that emulsify the fat, mostly removes the fatty acids at positions 1 and 3. This gives two free fatty acids and one 2-monoglyceride. Complete hydrolysis, as in saponification or with further lipase action, yields three fatty acid molecules and one glycerol molecule. So the end products are fatty acids together with glycerol, not just one of them.

Lipid Digestion and Triglyceride Breakdown:

Answer: (A) Stoichiometry

Explanation: The law of definite proportions (Proust’s law) states that a pure chemical compound always contains the same elements combined in the same fixed ratio by mass, regardless of its source or method of preparation. For example, water always has hydrogen and oxygen in a mass ratio of about 1:8. Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products, and it is built directly on this law along with the law of conservation of mass and the law of multiple proportions. Balanced equations, mole ratios and mass calculations all assume that compounds have fixed composition. Electrometry, photometry and spectrometry are analytical measurement techniques and not governed by a composition law.

Laws of Chemical Combination:

Answer: (C) Gallium

Explanation: Metalloids are elements with properties intermediate between metals and non-metals, and they are usually semiconductors. The commonly accepted metalloids are boron, silicon, germanium, arsenic, antimony and tellurium. Gallium is a true metal (group 13, p-block). It is soft and silvery with a very low melting point of about 29.8°C, so it melts in the hand, and it conducts electricity like a metal. Boron, silicon and germanium are all standard metalloids, so gallium is the one that is not.

Metalloids and Neighbouring Elements:

Answer: (A) 7.5-8.5

Explanation: The average pH of surface sea water is about 8.1, so it is slightly alkaline, and it normally varies between roughly 7.5 and 8.5 depending on location, temperature, depth and biological activity. This stability comes from the carbonate buffer system (CO₂, H₂CO₃, HCO₃⁻ and CO₃²⁻), which resists large pH changes. Ocean acidification is now lowering the average pH, from about 8.2 in pre-industrial times to about 8.1 today, because the oceans absorb extra atmospheric CO₂. Since the pH scale is logarithmic, this is roughly a 30% rise in hydrogen ion concentration.

pH of Common Natural Waters and Solutions:

Answer: (C) Chalk powder and water mixture

Explanation: The Tyndall effect is the scattering of a light beam by particles dispersed in a medium, which makes the beam’s path visible. It occurs only when the dispersed particles are large enough to scatter visible light, which means colloids and fine suspensions with particle sizes of roughly 1 nm to 1000 nm. Sugar, potash alum and potassium permanganate dissolve in water to form true solutions, where the particles are ions or molecules smaller than 1 nm and do not scatter light. Chalk powder does not dissolve. It forms a suspension of fine insoluble particles, and these scatter light strongly, so the beam is visible. Among the given options, this is the one most likely to show the effect.

Types of Mixtures and the Tyndall Effect:

Answer: (A) Black

Explanation: Copper(II) sulphide (CuS), also called covellite in its mineral form, is a black solid. It is formed as a black precipitate when H₂S gas is passed through an acidic solution of a copper(II) salt, for example Cu²⁺ + H₂S → CuS↓ + 2H⁺. This is the standard test for Group II cations in qualitative analysis, where Cu²⁺ is identified by this black precipitate. CuS is extremely insoluble in water (Ksp about 6 × 10⁻³⁶) and does not dissolve in dilute acids, which is why it precipitates even from acidic solution. It dissolves in hot dilute nitric acid.

Colours of Common Metal Sulphides:

Answer: (B) acetic acid

Explanation: Vinegar is a dilute aqueous solution of acetic acid (ethanoic acid, CH₃COOH). Table vinegar usually contains about 4 to 8% acetic acid by volume. It is made by the fermentation of ethanol-containing liquids such as fruit juice, malt or sugarcane juice. Yeast first converts sugar to ethyl alcohol, and then bacteria of the genus Acetobacter oxidise the alcohol to acetic acid in the presence of air: CH₃CH₂OH + O₂ → CH₃COOH + H₂O. Pure acetic acid freezes at about 16.6°C into ice-like crystals, which is why the undiluted form is called glacial acetic acid.

Vinegar and Related Acids:

Answer: (A) O₃

Explanation: Delocalized π electrons are π electrons that are spread over three or more atoms through resonance instead of sitting in a single bond. Ozone (O₃) is a bent molecule with two resonance structures, O=O⁺–O⁻ and ⁻O–O⁺=O. The π bond and the extra lone-pair electron density are shared across all three oxygen atoms, so both O–O bonds are identical, with a bond length of about 128 pm and a bond order of 1.5. This is why O₃ has delocalized π electrons. HCN (H–C≡N) and CO₂ (O=C=O) have localized π bonds, each confined between two atoms. CO is also described by localized bonding, so only ozone fits.

Molecules with Delocalized or Localized π Bonding:

Answer: (A) Starch

Explanation: A naturally occurring polymer is a macromolecule made by living organisms. Starch is a polysaccharide made of many α-D-glucose units joined by α-glycosidic bonds. Plants produce it as their food reserve, and it consists of two components: amylose (linear, α-1,4 linkages) and amylopectin (branched, with α-1,6 linkages at branch points). On complete hydrolysis it gives glucose. Teflon, neoprene and nylon are all synthetic polymers made in industry, so starch is the only natural polymer among the options.

Natural and Synthetic Polymers:

Answer: (A) reduction of lead

Explanation: When lead oxide is heated in a stream of hydrogen, hydrogen removes oxygen from the oxide: PbO + H₂ → Pb + H₂O. Lead(II) goes from an oxidation state of +2 in PbO to 0 in metallic lead, so it gains electrons and is reduced. Hydrogen goes from 0 to +1 in H₂O, so it is oxidised. PbO is therefore the oxidising agent and H₂ is the reducing agent. The reaction is a redox reaction, and since there is no chlorine source, PbCl₂ cannot form.

Reduction of Metal Oxides by Hydrogen:

Answer: (D) 60

Explanation: Fullerene is an allotrope of carbon made of closed cage-like molecules. The most common and best-known one is C₆₀ (buckminsterfullerene), which has 60 carbon atoms arranged as a truncated icosahedron, like a football. It has 12 pentagons and 20 hexagons. Each carbon is sp² hybridised and bonded to three others, with the fourth electron contributing to delocalised π bonding over the cage. It was discovered in 1985 by Harold Kroto, Robert Curl and Richard Smalley, who received the 1996 Nobel Prize in Chemistry. The name honours the architect Buckminster Fuller, whose geodesic domes have a similar shape.

Allotropes of Carbon:

Answer: (B) s < p < d < f

Explanation: Within a single principal energy level (same n), the energy of the subshells increases with the azimuthal quantum number l. In a multi-electron atom, electrons in an s orbital (l = 0) penetrate closest to the nucleus and feel the highest effective nuclear charge, so they are the lowest in energy. Penetration decreases for p (l = 1), d (l = 2) and f (l = 3), because they have more nodal planes and spend less time near the nucleus, and they are also shielded more by inner electrons. So the order is s < p < d < f. In a hydrogen-like atom with only one electron, all subshells of the same n have equal energy (they are degenerate). The order above holds only for multi-electron atoms.

Subshell Energy Order and Orbital:

Answer: (D) straight line

Explanation: For a real gas at constant temperature, the paper’s intended relation is Boyle’s law, PV = constant, which can be written as P = k(1/V). A graph of P against 1/V therefore passes through the origin as a straight line with slope k = nRT. The P vs V graph is a hyperbola, which is the commonly confused option. Real gases follow this only approximately, at low pressure and high temperature. At high pressure or low temperature, intermolecular attractions and the finite size of molecules cause deviations, so the line bends. The question assumes the ideal-like straight-line behaviour as the standard answer.

Gas Law Graphs at Constant Conditions:

Answer: (A) CF₄

Explanation: A 90° bond angle occurs in geometries where some bonds are perpendicular to others. CF₄ has a tetrahedral shape (sp³ carbon, no lone pairs), so all F–C–F angles are about 109.5°, and no 90° angle is present. PF₅ is trigonal bipyramidal, where the axial and equatorial bonds are at 90° (the equatorial bonds are 120° apart). SF₆ is octahedral, with all adjacent bonds at 90°. SiF₆²⁻ is also octahedral (sp³d² silicon), so it too has 90° angles. CF₄ is therefore the only species without a 90° angle.

Shapes and Bond Angles of Common Species:

Answer: (A) Radioactive Uranium

Explanation: The Chernobyl Unit 4 RBMK-1000 reactor used enriched uranium dioxide fuel (specifically the isotope U-235) to sustain the nuclear chain reaction. During a flawed power-test on 26 April 1986, a massive power surge caused the uranium fuel elements to rupture. This led to runaway fission, extreme steam explosions, and a massive graphite fire that breached the reactor core. While radioactive caesium (Caesium-137) and radioactive plutonium were released into the environment as hazardous byproducts of the explosion, they were generated by the fission process. The original metal fuel responsible for powering the reactor and driving the disaster was uranium.

Answer: (C) free delocalized electrons

Explanation: In graphite, each carbon atom is sp² hybridised and bonded to three other carbons in flat hexagonal layers. The fourth valence electron of each carbon is not used in a localized bond. These electrons form a delocalized π cloud spread over the whole layer and are free to move along the plane when a potential difference is applied. This mobility makes graphite a good electrical conductor, unlike diamond, where all four electrons are locked in localized sp³ bonds. The layers are held together only by weak van der Waals forces, so they slide over each other easily, which also makes graphite soft and slippery.

Graphite vs Diamond and Other Conductors:

Answer: (A) Brine

Explanation: Brine is a concentrated aqueous solution of sodium chloride. When it is heated, the water evaporates and the dissolved salt, being non-volatile, stays behind as a solid white residue. Bromine and mercury are pure elements that are liquid at room temperature. They vaporise completely on heating and leave nothing behind, and mercury does so only at its boiling point of about 357°C. Alcohol (ethanol) is a pure, volatile liquid that boils at about 78°C and evaporates fully. Only brine, a solution containing a non-volatile solute, leaves a residue.

Liquids and Their Behaviour on Heating:

Answer: (C) Al

Explanation: Aluminium paint is made from finely powdered aluminium metal suspended in a drying oil or varnish. The metal flakes “leaf” and overlap on the surface as the oil dries, forming a shiny, silvery layer. This layer reflects heat and light and acts as a barrier against moisture and air. Aluminium also forms a thin, tough oxide film that protects it from corrosion. For these reasons, the paint is widely used on iron and steel structures, storage tanks, pipelines, radiators and bridges. Iron and tin powders would rust or lack the reflective finish, and silver is far too costly.

Metal Powders and Pigments Used in Paints:

Answer: (C) Chlorine

Explanation: DDT (dichlorodiphenyltrichloroethane, (ClC₆H₄)₂CH-CCl₃) is an organochlorine insecticide. Bleaching powder (CaOCl₂, calcium oxychloride) is made by passing chlorine gas over slaked lime: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O. Both compounds contain chlorine, and it is the active element in each. In DDT it is bonded covalently to carbon, and in bleaching powder it provides the OCl⁻ (hypochlorite) and Cl⁻ ions responsible for bleaching and disinfecting. Sulphur, phosphorus and arsenic are not part of either compound.

Chlorine-Containing Compounds:

Answer: (D) Aspergillus niger

Explanation: Citric acid is produced industrially by aerobic fermentation of sugar-rich raw materials such as crude sugar, molasses or starch hydrolysate, using the mould Aspergillus niger. The fungus takes up sugar and, under controlled conditions (low pH of about 2 to 3, high sugar concentration, limited trace metals such as iron and manganese, and plenty of air), it converts the sugar to citric acid through the Krebs cycle and releases it into the medium. The acid is then recovered by precipitating it as calcium citrate and treating that with sulphuric acid. The question says “enzyme”, but Aspergillus niger is a microorganism and not an enzyme. It is the intended answer, since amylase and lipase do not make citric acid and Thiobacilli are sulphur-oxidising bacteria.

Microorganisms in Industrial Fermentation:

Answer: (D) Reduce plasticity and quick setting of cement paste

Explanation: Gypsum (CaSO₄·2H₂O), about 2 to 5% by weight, is interground with cement clinker to control the setting time. Without it, tricalcium aluminate (C₃A) in the clinker reacts almost instantly with water and the paste stiffens in minutes (flash set), leaving no time to mix, transport and place it. Gypsum reacts with C₃A and water to form a protective layer of ettringite (calcium sulphoaluminate) on the C₃A grains. This slows the reaction, so the paste sets in a controlled way, with initial setting not earlier than 30 minutes and final setting within about 10 hours (IS code). So gypsum acts as a set retarder. It prevents flash set and reduces the quick stiffening that would make the paste unworkable.

Cement: Compounds, Additives and Setting Details

Answer: (D) YBa₂Cu₃O₇

Explanation: Superconductors lose all electrical resistance below a critical temperature (Tc) and also stop superconducting above a critical magnetic field (Hc). YBa₂Cu₃O₇ (YBCO) is a high-temperature ceramic superconductor with Tc of about 92 K, which is above the boiling point of liquid nitrogen (77 K). Its upper critical field is also very large (well over 100 tesla at low temperature). Lead has Tc of 7.2 K, Nb-Zr alloy about 10 K and Nb₃Ge about 23 K, and all of them have lower critical fields. So YBCO has both the highest critical temperature and the highest critical magnetic flux density among the options.

Superconducting Materials:

Answer: (D) All of the above

Explanation: Thin layer chromatography (TLC) separates the components of a mixture on a thin layer of adsorbent (usually silica gel or alumina) coated on a glass or plastic plate. The sample is spotted near the bottom, and a solvent rises by capillary action. Components travel at different rates depending on how strongly they are adsorbed and how soluble they are in the solvent, and each is identified by its Rf value (distance moved by the spot divided by distance moved by the solvent front). In clinical and forensic laboratories, TLC is a quick, cheap screening method. It is used to detect illicit drugs (such as opiates, amphetamines and cannabinoids), poisons (such as alkaloids, pesticides and toxic plant compounds) and ink dyes in questioned documents. Since all three are identified by TLC, the answer is “All of the above”.

Thin Layer Chromatography:

Answer: (D) Ni-Zn ferrite

Explanation: An induction core (as in inductors, transformers and high-frequency coils) must have high magnetic permeability, low coercivity and very high electrical resistivity, so that eddy-current losses stay small at high frequency. Soft ferrites such as Ni-Zn ferrite (and Mn-Zn ferrite) are ceramic, magnetically soft and highly resistive (about 10⁶ to 10⁹ Ω·cm), so they work well as cores at radio frequencies. AlNico and Ba-Sr ferrite are magnetically hard materials, with high coercivity, and are used as permanent magnets. Garnets are used in microwave devices and not as induction cores.

Magnetic Materials:

Answer: (C) Methyl Salicylate

Explanation: Oil of wintergreen is methyl salicylate (methyl 2-hydroxybenzoate, C₈H₈O₃). It was originally obtained by steam distillation of the leaves of the wintergreen plant (Gaultheria procumbens), and it is now mostly made synthetically by esterifying salicylic acid with methanol in the presence of an acid catalyst. It is a colourless to pale yellow liquid with a strong, sweet minty smell. It is used as a flavouring, in liniments and balms for muscle and joint pain (it acts as a counter-irritant), and in perfumery. It is toxic if swallowed in quantity. Acetic acid, benzoic acid and phthalic acid are different acids and are not the oil of wintergreen.

Methyl Salicylate and Related Compounds:

Answer: (D) Aqueous H₂O₂

Explanation: Green chemistry aims to reduce or eliminate hazardous substances and waste. Aqueous hydrogen peroxide is the preferred clean oxidising agent because its only by-product is water: H₂O₂ → H₂O + [O]. It leaves no toxic metal residues and is easy to handle in dilute form. K₂Cr₂O₇ produces toxic, carcinogenic chromium(VI) and chromium(III) waste. K₂S₂O₈ leaves sulphate salts as by-products. NH₄NO₃ is not a clean oxidant and has explosion hazards. H₂O₂ is therefore the green oxidant of choice, used in pulp bleaching, wastewater treatment and catalytic oxidations (for example, epoxidation and the Baeyer-Villiger reaction).

Oxidising Agents:

Answer: (C) coarsening effect from Ostwald ripening or agglomeration on aging.

Explanation: Nanomaterials have very high surface area to volume ratios, so their surface energy is high and they are thermodynamically unstable. Over time, small particles dissolve and redeposit onto larger ones (Ostwald ripening), or they stick together (agglomeration) to lower their surface energy. This coarsening destroys the nanoscale size and the special properties that depend on it, such as optical, catalytic and magnetic behaviour. It is therefore the main practical hindrance in making and storing nanomaterials. Large surface area to volume ratio, uniform size distribution and even morphology are desirable features, not drawbacks. Stabilisers such as capping agents, surfactants or polymer coatings are used to prevent coarsening.

Nanomaterials:

Answer: (A) (BN)₃

Explanation: Boron nitride (BN) is isoelectronic with carbon: a B–N pair has the same number of valence electrons as a C–C pair. Hexagonal boron nitride has the same layered structure as graphite, with flat sheets of alternating B and N atoms in hexagonal rings (sp² hybridised), held together by weak van der Waals forces. Because it looks like graphite and is soft and slippery, it is called “inorganic graphite” or “white graphite”. Unlike graphite, it is a white electrical insulator, since the π electrons are held on the nitrogen atoms and are not free to move. B₃N₃H₆ (borazine) is a different compound, called “inorganic benzene”. Si₃N₄ is a hard ceramic, not a layered solid.

Boron Nitride and Inorganic Analogues of Carbon Compounds:

Answer: (B) Concrete

Explanation: Concrete is a hardened mass made by mixing cement, fine aggregate (sand), coarse aggregate (stone chips or gravel) and water in suitable proportions. The cement and water form a paste that coats the aggregates and binds them together as it sets and hardens through hydration. This gives a strong, durable material that resists compression well. Mortar is only cement (or lime), sand and water, with no coarse aggregate, and is used for joining bricks and plastering. Reinforced Cement Concrete (RCC) is concrete with steel bars embedded in it, so it needs steel in addition to the ingredients named here.

Cement-Based Materials:

Answer: (D) All of the above

Explanation: Zone refining is a method of ultra-purification based on the fact that impurities are more soluble in the molten phase than in the solid phase of a metal. A narrow heater moves slowly along a rod of the impure material and melts a thin zone. As the zone moves forward, pure material solidifies behind it, while the impurities are carried along in the molten zone and collect at one end, which is later cut off. Repeating the pass several times gives extremely pure material. The method is used for semiconductor-grade silicon and germanium (impurity levels of parts per billion), and also for gallium, which has a low melting point and is purified in the same way. Since all three are purified by zone refining, the answer is “All of the above”.

Zone Refining:

Answer: (D) Directionality

Explanation: A metallic bond is the attraction between positive metal ions and a “sea” of delocalized valence electrons that move freely through the whole lattice. Because this electron sea is spread evenly in all directions, the bond is non-directional. This explains the typical properties of metals: opacity and lustre (free electrons absorb and re-emit light), ductility and malleability (layers of ions can slide without breaking the bond, since the electron sea keeps holding them together), and high electrical and thermal conductivity (mobile electrons carry charge and heat). Directionality is a feature of covalent bonds, where electrons are shared along a fixed line between two atoms. So it is the one property that metallic bonding does not have.

Metallic vs Other Types of Bonding:

Answer: (A) Cu & Zn

Explanation: Brass is an alloy of copper and zinc. Zinc is usually 5 to 45% by weight, and varying the proportion changes the colour, strength and ductility. More zinc makes the alloy harder, stronger and more yellow, while less zinc gives a reddish, softer and more corrosion-resistant brass. Brass is a substitutional alloy, since zinc atoms replace copper atoms in the lattice. It is easy to cast and machine, resists corrosion and has an attractive gold-like appearance. Bronze is copper and tin, and the other options do not describe brass.

Common Alloys:

Answer: (B) K₂Cr₂O₇

Explanation: A primary standard is a substance pure and stable enough to prepare a solution of exactly known concentration by weighing it directly. It must be available in very high purity (99.9% or better), be stable in air (not absorb moisture or CO₂, and not be oxidised), have a high molar mass to reduce weighing error, be soluble in water, and react completely and in a fixed ratio. Potassium dichromate is non-hygroscopic, can be dried at about 150°C, and its solutions are stable for years, so it is widely used as a primary standard in redox titrations (for example, the standardisation of ferrous salts and thiosulphate). KMnO₄ is always slightly contaminated with MnO₂ and decomposes in light, so it is a secondary standard. Sodium thiosulphate is hydrated and its solution slowly decomposes, and EDTA (as the free acid) is generally standardised against zinc or CaCO₃. Note that the disodium salt of EDTA can be used as a primary standard when it is carefully dried, but K₂Cr₂O₇ is the intended answer.

Primary and Secondary Standards:

Answer: (B) β particle

Explanation: Carbon-14 dating works because ¹⁴C is a radioactive isotope formed in the upper atmosphere when cosmic-ray neutrons strike nitrogen-14: ¹⁴₇N + ¹₀n → ¹⁴₆C + ¹₁H. Living organisms keep taking in carbon, so their ¹⁴C level stays in balance with the atmosphere. After death the intake stops, and ¹⁴C decays by beta-minus emission: ¹⁴₆C → ¹⁴₇N + ⁰₋₁e (β particle) + antineutrino. Its half-life is 5730 years. Measuring the remaining ¹⁴C activity in a sample gives its age, and the method works up to about 50,000 years.

Radioisotopes Used in Dating and Their Emissions:

Answer: (C) its greater affinity for O₂

Explanation: Thermit welding uses a mixture of aluminium powder and iron(III) oxide: Fe₂O₃ + 2Al → Al₂O₃ + 2Fe + heat. Aluminium has a much greater affinity for oxygen than iron does, so it strips oxygen from the iron oxide in a highly exothermic reaction. The heat released raises the temperature to about 2500°C, enough to produce molten iron. This molten iron flows into the gap between the rail ends or metal parts being joined and fuses them on solidifying. Aluminium’s lightness and melting point are not the reason it is chosen, so “All of the above” is not correct.

Thermit Reaction:

Answer: (B) Starch and (C) Glycogen (both are correct; the question was cancelled by the PSC)

Explanation: A polysaccharide is a carbohydrate made of many monosaccharide units joined by glycosidic bonds, and it gives many sugar molecules on hydrolysis. Starch is a plant storage polysaccharide made of α-D-glucose units. Glycogen is the animal storage polysaccharide, also made of α-D-glucose, but more highly branched. Both fit the definition, so the question had two correct options, which is why the commission cancelled it. Glucose is a monosaccharide and sucrose is a disaccharide (glucose + fructose), so neither is a polysaccharide.

Classification of Carbohydrates:

Answer: (B) H₂CO₃ and NaHCO₃

Explanation: Blood pH is held at about 7.35 to 7.45 mainly by the carbonic acid-bicarbonate buffer, made of H₂CO₃ (weak acid) and NaHCO₃ (its conjugate base salt). If extra acid (H⁺) enters the blood, bicarbonate neutralises it: HCO₃⁻ + H⁺ → H₂CO₃, which breaks down to CO₂ and water and is exhaled by the lungs. If extra base enters, H₂CO₃ neutralises it: H₂CO₃ + OH⁻ → HCO₃⁻ + H₂O. The kidneys also adjust bicarbonate levels. Na₂CO₃ is a strong base salt and does not form a buffer with H₂CO₃. The acetic acid pair is not found in blood, and the phosphate pair is important mainly inside cells and in urine.

Buffer Systems in the Human Body:

Answer: (D) liquified petroleum gas

Explanation: Calorific value is the heat released on complete combustion of a unit mass of fuel. Among the gaseous fuels listed, LPG (a mixture of propane and butane) has the highest value, about 46 to 50 MJ/kg (roughly 90 to 120 MJ/m³). It is made of larger hydrocarbon molecules, which have more C–H and C–C bonds to burn. Natural gas (mostly methane) gives about 50 MJ/kg by mass but a lower value by volume (about 36 to 40 MJ/m³). Producer gas (about 4 to 6 MJ/m³) and water gas (about 10 to 12 MJ/m³) are low because they consist largely of CO, H₂ and, in producer gas, non-combustible N₂. The paper’s key notes 46.1 MJ/kg for the correct answer, which matches LPG.

Gaseous Fuels:

Answer: (A) ²₁H + ³₁H → ⁴₂He + ¹₀n

Explanation: Nuclear fusion is the joining of two light nuclei to form a heavier nucleus, with a large release of energy. Option (A) combines deuterium (²₁H) and tritium (³₁H) to give helium-4 and a neutron, releasing about 17.6 MeV. It needs extremely high temperatures (about 10⁸ K) to overcome the repulsion between the positively charged nuclei. This is the reaction pursued in fusion reactors such as ITER. Option (C) is fission: a heavy uranium-235 nucleus absorbs a neutron and splits into barium and krypton plus three neutrons. Options (B) and (D) are nuclear transmutation reactions, in which a nucleus captures or exchanges a particle without large-scale fusion or fission.

Nuclear Reactions:

Answer: (D) midway between liquid and gas

Explanation: A supercritical fluid is a substance held at or above both its critical temperature and critical pressure. For CO₂ these are 31.1°C and 73.8 bar (7.38 MPa). Above this point, the distinction between liquid and gas disappears and only one phase exists. Supercritical CO₂ has a density close to that of a liquid, so it dissolves substances well like a liquid. It also has a low viscosity and high diffusivity close to those of a gas, so it penetrates porous solids easily. It has no surface tension. This combination is why its properties are described as midway between liquid and gas. It is non-toxic, non-flammable and cheap, and it leaves no solvent residue because it turns into a gas when the pressure is released.

Supercritical Fluids:

Answer: (D) Activation energy of the reaction

Explanation: A catalyst speeds up a reaction by providing an alternative pathway with a lower activation energy. More reactant molecules then have enough energy to react, so the rate rises. The catalyst does not change the energy of the reactants or products, so the potential energy of both stays the same. It also does not change the heat of reaction (ΔH) or the equilibrium position. It lowers the activation energy of the forward and reverse reactions equally, so equilibrium is reached faster, but the equilibrium constant is unchanged. The catalyst is not used up, since it is regenerated at the end of the reaction.

Catalysts:

Answer: (D) Urea

Explanation: A colloid is a heterogeneous mixture in which particles of 1 nm to 1000 nm are dispersed in a medium and do not settle or pass through a semipermeable membrane. Milk is an emulsion (liquid fat dispersed in water), smoke is an aerosol (solid particles in air), and blood is a colloidal dispersion of cells and proteins in plasma. Urea (NH₂CONH₂) is a small molecule that dissolves in water to form a true solution, with particles well below 1 nm. It is a crystalloid, so it is not a colloid.

Colloids and Related Systems:

Answer: (D) Vanillin

Explanation: Vanillin (4-hydroxy-3-methoxybenzaldehyde, C₈H₈O₃) is the main flavour compound of vanilla beans. It is widely used to flavour ice cream, chocolate, bakery products and drinks, and as a fragrance in perfumes and soaps. Natural vanillin comes from the cured pods of Vanilla planifolia, but most of the world’s supply is made synthetically from guaiacol or lignin. Carboxymethyl cellulose is a thickener and stabiliser, ascorbic acid is vitamin C used as an antioxidant, and saccharin is an artificial sweetener, so none of these is mainly a flavour or perfume ingredient.

Food Additives and Flavouring Compounds:

Answer: (A) Sulphur

Explanation: Ultramarine blue is a deep blue pigment, originally made by grinding the semi-precious stone lapis lazuli, and now made synthetically by heating kaolin clay, sodium carbonate, sulphur and a reducing agent (charcoal or resin). Its formula is approximately Na₈[Al₆Si₆O₂₄]S₂ to Na₈[Al₆Si₆O₂₄]S₄. It is a sodium aluminosilicate framework (sodalite-type) that traps sulphur species inside its cages. The blue colour comes from the polysulphide radical anion S₃⁻, which absorbs light at about 600 nm. The pigment is stable to light and alkalis but is decomposed by acids, which release hydrogen sulphide. Cobalt is the basis of a different blue pigment, cobalt blue, and phosphorus and boron are not part of ultramarine.

Blue Pigments and Their Composition:

Answer: (D) All of the above

Explanation: Tungsten carbide (WC) is a hard interstitial carbide in which small carbon atoms occupy the gaps in a close-packed tungsten lattice. Its bonding is a mixture of all three types. The W–C bonds are strongly covalent and directional, which gives extreme hardness (about 9 on the Mohs scale). There is a degree of ionic character because of the electronegativity difference between carbon and tungsten, with some charge transfer. The tungsten atoms also share a delocalised electron sea, which is metallic bonding and explains why WC conducts electricity and has a metallic lustre. So no single bond type describes it, and “All of the above” is the answer.

Interstitial Carbides and Other Hard Materials:

Answer: (D) Detergent is fully biodegradable.

Explanation: Unlike soaps (which are made from natural fats and are fully biodegradable), many synthetic detergents contain highly branched hydrocarbon chains derived from petroleum. Bacteria cannot easily break down these branched structures, making them non-biodegradable or only partially biodegradable. This can lead to environmental issues like water pollution and foaming in water bodies.

The other statements correct

• (A) & (B): Detergents are sodium salts of long-chain alkyl hydrogen sulphates or benzene sulphonic acids. Their charged ends do not form insoluble precipitates (scum) with the calcium and magnesium ions found in hard water. Because they form soluble salts, they work well and do not form a precipitate in hard water.
• (C): Detergents are formulated to be highly soluble in water, allowing them to lather much more easily than traditional soap.

Answer: (B) UO₂

Explanation: Fuel rods in a nuclear reactor contain the fissile material, and the most common fuel form is uranium dioxide (UO₂), made into small ceramic pellets and stacked inside sealed zirconium alloy tubes. UO₂ has a very high melting point (about 2865°C), is chemically stable, does not react with water or the cladding, and retains fission products well. Graphite is used as a moderator in some reactors, and D₂O (heavy water) is both a moderator and a coolant. ZrO₂ is not a fuel. Zirconium metal alloys (Zircaloy) are used as the cladding that encloses the fuel, because zirconium absorbs very few neutrons.

Nuclear Reactor Materials:

Answer: (B) Quenching

Explanation: Quenching is the rapid cooling of a hot metal, usually steel, by plunging it into water, oil, brine or air. Steel is first heated above its critical temperature (about 800 to 900°C), where its structure is austenite. Rapid cooling traps carbon in the iron lattice before it can form the soft equilibrium phases. This produces martensite, which is very hard but brittle, with internal stresses. Annealing is the opposite: very slow cooling (usually in the furnace) that softens the metal and relieves stress. Tempering is gentle reheating of quenched steel to reduce its brittleness.

Heat Treatment Processes of Steel:

Answer: (C) K₂SO₄·Al₂(SO₄)₃·24H₂O

Explanation: A double salt is formed by crystallising two simple salts together in a fixed ratio. It exists only in the solid state and breaks up into all its individual ions when dissolved in water, so its solution shows the tests of each ion. K₂SO₄·Al₂(SO₄)₃·24H₂O is potash alum. In water it gives K⁺, Al³⁺ and SO₄²⁻ ions. K₄[Fe(CN)₆] is a complex salt, because it keeps the [Fe(CN)₆]⁴⁻ ion intact in solution and does not give the test for Fe²⁺ or CN⁻. FeSO₄·6H₂O is a simple hydrated salt (the standard form is FeSO₄·7H₂O), and Pb(OH)NO₃ is a basic salt.

Types of Salts:

Answer: (A) Al

Explanation: Bayer’s process is the method for extracting pure alumina (Al₂O₃) from bauxite, the chief ore of aluminium. Crushed bauxite is digested with hot concentrated sodium hydroxide solution (about 150 to 200°C under pressure). Alumina dissolves as sodium aluminate, while impurities such as iron oxide (red mud) and silica stay behind and are filtered off. The clear solution is cooled, diluted and seeded with Al(OH)₃ crystals, which makes aluminium hydroxide precipitate. This is heated (calcined) at about 1000°C to give pure alumina. The alumina is then electrolysed in molten cryolite by the Hall-Héroult process to obtain aluminium metal, so the metal extracted from bauxite is Al.

Bayer’s Process and Aluminium Extraction:

Answer: (D) Stainless Steel

Explanation: Passivation is the formation of a thin, invisible, adherent and self-healing oxide film on a metal surface that makes the metal inert and stops further corrosion. Stainless steel contains at least about 10.5 to 12% chromium. The chromium reacts with oxygen to form a very thin layer of chromium(III) oxide (Cr₂O₃, only a few nanometres thick). If the surface is scratched, the film re-forms immediately in the presence of oxygen. The metal is therefore protected by passivation. Mild steel rusts freely because its iron oxide layer is porous and flaky and does not protect. Silver tarnishes by forming black Ag₂S, and bronze develops a green patina, and neither forms a passivating film of this kind.

Passivation:

Answer: (B) PVᵞ = constant

Explanation: In an adiabatic process no heat enters or leaves the gas (Q = 0), so any work done by the gas during expansion comes from its internal energy and the temperature falls. For a reversible adiabatic change of an ideal gas, applying the first law with PV = nRT gives PVᵞ = constant, where γ = Cp/Cv. Because γ is greater than 1, the pressure falls faster during adiabatic expansion than during isothermal expansion (where PV = constant). The related forms are TVᵞ⁻¹ = constant and T^γ P^(1−γ) = constant. The form PVᵞ⁻¹ = constant is not valid, and PV^(1/γ) = constant is also incorrect.

Adiabatic and Other Gas Processes:

Answer: (B) 1.40

Explanation: The ratio γ = Cp/Cv depends on the degrees of freedom (f) of the gas molecule: γ = 1 + 2/f. A diatomic gas at ordinary temperature has 5 degrees of freedom (3 translational and 2 rotational), so Cv = 5R/2 and Cp = Cv + R = 7R/2. Then γ = (7R/2)/(5R/2) = 7/5 = 1.40. Vibrational modes are not excited at ordinary temperatures, so they are left out. At very high temperatures vibration becomes active (f = 7), and γ falls to about 1.29.

Specific Heat Ratio of Gases:

Answer: (D) All of the above

Explanation: Natural polymers are macromolecules produced by living organisms. Proteins are polymers of α-amino acids joined by peptide bonds. Cellulose is a polymer of β-D-glucose units joined by β-1,4-glycosidic bonds. Natural rubber is a polymer of isoprene (cis-1,4-polyisoprene), obtained as latex from the rubber tree. All three occur in nature, so each belongs to the class of natural polymers.

Natural Polymers:

Answer: (B) Azeotrope

Explanation: An azeotrope is a liquid mixture that boils at a constant temperature and gives a vapour with the same composition as the liquid. It therefore behaves like a single pure component during boiling and cannot be separated into its parts by ordinary distillation. It arises from deviations from Raoult’s law. A positive deviation gives a minimum-boiling azeotrope (for example ethanol-water, about 95.6% ethanol, boiling at 78.2°C). A negative deviation gives a maximum-boiling azeotrope (for example HNO₃-water, about 68% HNO₃, boiling at 120.5°C). A eutectic is a solid-liquid mixture that melts at a single temperature, not a boiling mixture. The spelling in the paper, “Azotrope”, means azeotrope.

Azeotropes and Related Mixtures:

Answer: (D) F

Explanation: Electronegativity is the ability of an atom to attract the shared electron pair in a covalent bond. Along a period it rises from left to right, and down a group it falls, because atomic size grows and the nuclear pull on bonding electrons weakens. Fluorine sits at the top of the halogen group and is the smallest halogen, so it has the highest electronegativity of all elements, 3.98 on the Pauling scale. The order among the halogens is F > Cl > Br > I.

Electronegativity of Halogens and Related Elements:

Answer: (A) Solid CO₂

Explanation: Dry ice is the solid form of carbon dioxide. At normal atmospheric pressure, CO₂ does not melt into a liquid. It sublimes directly from solid to gas at −78.5°C, leaving no wet residue, which is why it is called “dry”. Liquid CO₂ exists only above about 5.1 atm pressure, at the triple point of −56.6°C. Dry ice is made by compressing and cooling CO₂ gas until it liquefies, then letting the pressure drop suddenly, which cools the gas so much that part of it freezes into snow-like solid that is pressed into blocks. It is used for refrigeration and preserving ice cream, vaccines and food in transit, for producing fog effects on stage, and for dry blasting cleaning.

Dry Ice and Related Cooling Agents:

Answer: (A) Allotrope

Explanation: Allotropes are different structural forms of the same element in the same physical state, which differ in how the atoms are arranged and therefore in their physical properties. Carbon exists as diamond (sp³ tetrahedral network), graphite (sp² layers), amorphous carbon (coal, charcoal, soot), fullerenes and graphene. All of these are made of carbon atoms only, so they are allotropes of carbon. Isomers are compounds with the same molecular formula but different structures. Isotopes are atoms of the same element with different mass numbers, and isobars are atoms of different elements with the same mass number.

Allotropy and Related Terms:

Answer: (C) colloidal particles from crystalloids.

Explanation: Dialysis is a purification method that separates colloidal particles from dissolved crystalloids (small ions and molecules) using a semipermeable membrane such as parchment paper, cellophane or animal bladder. The impure colloidal sol is placed in a bag made of the membrane and suspended in pure, flowing water. Crystalloids such as salts, sugar and urea are small enough to pass through the pores of the membrane into the water, while the larger colloidal particles (1 nm to 1000 nm) are held back. Repeated changes of water remove the electrolytes completely, which also helps stabilise the sol. The same principle is used in the artificial kidney (haemodialysis), where urea and excess salts are removed from the blood while blood cells and proteins stay.

Dialysis and Related Separation Methods:

Answer: (B) Cd

Explanation: Control rods regulate the chain reaction in a nuclear reactor by absorbing neutrons. Cadmium has a very large neutron absorption cross-section, especially for slow (thermal) neutrons, so inserting cadmium rods into the core reduces the number of neutrons available to cause fission and slows the reaction. Withdrawing them lets the reaction speed up, and full insertion shuts the reactor down. Graphite is used as a moderator to slow neutrons down, not to absorb them. Beryllium acts as a neutron reflector and moderator, and copper has poor neutron absorption, so neither works as a control rod.

Control Rod and Other Reactor Materials:

Answer: (D) Fusion process

Explanation: The Sun gets its radiant energy from nuclear fusion in its core, where the temperature is about 15 million K and the pressure is enormous. Hydrogen nuclei (protons) fuse to form helium by the proton-proton chain: four protons combine to give one helium-4 nucleus, two positrons and two neutrinos, releasing about 26.7 MeV per helium nucleus formed. A small part of the mass is converted into energy according to E = mc². The Sun converts about 4 million tonnes of matter into energy every second, and this energy slowly moves out to the surface and is radiated as light and heat. Fission needs heavy nuclei such as uranium, which the Sun lacks, and radioactive disintegration and the photoelectric effect cannot supply this energy.

Energy Generation in Stars:

Answer: (A) Teflon

Explanation: Teflon is polytetrafluoroethylene (PTFE), a polymer of tetrafluoroethylene (CF₂=CF₂), made by free-radical addition polymerisation. The C–F bond is very strong and the fluorine atoms form a tight protective sheath around the carbon chain, so PTFE is chemically inert, resists heat up to about 260°C and has a very low coefficient of friction. Few substances stick to it, which is why it is used to coat non-stick frying pans. Perspex is polymethyl methacrylate (a transparent glass substitute), Bakelite is a hard thermosetting phenol-formaldehyde resin, and Orlon is polyacrylonitrile, used as an artificial wool.

Common Synthetic Polymers:

Answer: (D) Chlorination

Explanation: Chlorination is the addition of chlorine, or a chlorine compound such as bleaching powder or sodium hypochlorite, to water in order to kill disease-causing bacteria and other microorganisms that remain after sedimentation, coagulation and filtration. Chlorine reacts with water to form hypochlorous acid and hypochlorite ions: Cl₂ + H₂O → HOCl + H⁺ + Cl⁻, and HOCl ⇌ H⁺ + OCl⁻. HOCl is the main disinfecting agent. It is a small neutral molecule that passes through the cell wall of microbes and oxidises their enzymes, which kills them. A small amount of “residual chlorine” (about 0.2 to 0.5 mg/L) is kept in the water so that it stays safe in the supply pipes. Sedimentation, coagulation and filtration only remove suspended and colloidal matter and do not reliably kill bacteria.

Water Treatment Steps and Disinfectants:

Answer: (C) Na₂CO₃·10H₂O

Explanation: Washing soda is sodium carbonate decahydrate, Na₂CO₃·10H₂O. It is made by recrystallising anhydrous sodium carbonate (soda ash) from water, and the crystals carry ten molecules of water of crystallisation. Anhydrous Na₂CO₃ is soda ash, and NaHCO₃ is baking soda. On exposure to air the crystals lose water and turn into a white powder, the monohydrate Na₂CO₃·H₂O, which is called efflorescence. Washing soda is alkaline in water because the carbonate ion hydrolyses, which helps remove grease and also removes permanent hardness from water by precipitating calcium and magnesium as carbonates. The paper’s hint “(Sodium carbonate)” fits option (A) loosely, but the compound known specifically as washing soda is the decahydrate.

Sodium Compounds in Daily Use:

Answer: (C) particle size and surface area

Explanation: The action of a catalyst depends on its physical state and especially its surface. In heterogeneous catalysis, the reaction takes place on the surface of the solid catalyst, where reactant molecules are adsorbed, react, and then leave. A finely divided catalyst has a much larger surface area, so it offers more active sites and a faster rate. This is why catalysts are used as powders, gauzes or on porous supports, and why platinum gauze or finely divided nickel works better than lumps. The catalyst’s mass in bulk, or its solubility, does not control its action.

Factors Affecting Catalyst Action:

Answer: (B) emulsification

Explanation: A soap molecule has a long hydrocarbon tail that is hydrophobic (water-hating, oil-loving) and a carboxylate head (–COO⁻Na⁺) that is hydrophilic (water-loving). In water, the tails dissolve into the grease or oil on a dirty surface while the heads stay in the water. The soap breaks the grease into tiny droplets, each surrounded by soap molecules with their negative heads pointing outward. These structures are called micelles. The negative charges repel each other, so the droplets stay dispersed in the water as a stable emulsion and do not rejoin. They are then rinsed away with the water. This process is emulsification, which is different from absorption or coagulation.

Soap Action and Related Terms:

Answer: (B) Gamma ray

Explanation: Among alpha, beta, and gamma radiations, gamma rays have the highest penetrating power. They are high-energy electromagnetic photons with no mass or charge, allowing them to effortlessly pass straight through skin, tissues, and bones. While an alpha particle has a higher ionizing power up close, it cannot even penetrate the outer layer of human skin. Gamma rays, however, can reach deep internal organs and cells throughout the entire body. Once inside, they ionize molecules, shatter cell structures, and mutate DNA, which directly triggers cell death, organ failure, and malignant cancers.

Comparison of Ionizing vs. Penetrating Effects:

Answer: (D) Thorium

Explanation: Monazite is a reddish-brown phosphate mineral, (Ce, La, Nd, Th)PO₄, and it is the main commercial ore of thorium. It also contains rare earth elements (cerium, lanthanum, neodymium) and typically 5 to 10% thorium oxide (ThO₂), sometimes up to about 20%. It occurs in beach and river sands, formed by the weathering of granite and gneiss rocks, and is concentrated by gravity, magnetic and electrostatic separation. India has some of the world’s largest monazite reserves, mainly in the beach sands of Kerala, Tamil Nadu, Odisha and Andhra Pradesh. Thorium from monazite is the basis of India’s three-stage nuclear power programme, where Th-232 is converted into fissile U-233 in a reactor.

Important Ores and Minerals of Radioactive and Rare Elements:

Answer: (C) Sucrose

Explanation: A reducing sugar has a free aldehyde group or a free hemiacetal (or ketone-forming) group that can open up in solution and reduce Tollens’ reagent, Fehling’s solution and Benedict’s solution. Glucose has a free aldehyde group. Maltose and lactose are disaccharides in which one of the two units still has a free hemiacetal –OH, so they can open to the aldehyde form and reduce these reagents. In sucrose, the anomeric carbon of glucose (C-1) is joined to the anomeric carbon of fructose (C-2) through an α,β-1,2-glycosidic bond. Both reducing centres are tied up in the bond, so no free aldehyde or ketone group is available, and sucrose does not reduce Fehling’s or Tollens’ reagent.

Reducing and Non-Reducing Sugars:

Answer: (C) barium

Explanation: In fireworks, colours come from the emission of light by metal ions when they are heated in the flame. Electrons in the metal atoms are excited by the heat and then fall back to lower energy levels, releasing light of a wavelength characteristic of that metal. Barium compounds (such as barium nitrate, Ba(NO₃)₂, or barium chloride) give a bright green flame, from emission bands at about 510 to 530 nm. Barium nitrate also acts as an oxidiser in the mixture. Sodium gives yellow, potassium gives lilac or violet, and mercury is not used for colour in fireworks because its compounds are toxic.

Flame Colours of Metals in Fireworks:

Answer: (B) EDTA method

Explanation: The hardness of water is caused by dissolved calcium and magnesium salts, and it is estimated by complexometric titration with EDTA (ethylenediaminetetraacetic acid, C₁₀H₁₆N₂O₈, usually used as its disodium salt). The water sample is buffered to pH about 10 with an ammonia-ammonium chloride buffer, and a few drops of Eriochrome Black T indicator are added. The indicator forms an unstable wine-red complex with Ca²⁺ and Mg²⁺. During titration, EDTA binds these ions in a stable 1:1 complex, and at the end point it removes the metal from the indicator, so the colour changes from wine red to blue. The volume of EDTA used gives the total hardness. “Titrimetric method” is the general category, but the specific standard method for hardness is EDTA titration.

Methods for Estimating Hardness of Water:

Answer: (C) Bakelite

Explanation: A thermosetting plastic is a polymer that softens and can be moulded only once. On first heating it undergoes a chemical change, forming strong cross-links between the chains into a rigid three-dimensional network. Once set, it cannot be softened or remoulded by reheating, and it chars on strong heating. Bakelite, made by condensation of phenol and formaldehyde, is the classic example: hard, heat resistant and an electrical insulator. PVC and PVA (polyvinyl acetate) are thermoplastics. They have linear or slightly branched chains and soften on heating, so they can be melted and reshaped repeatedly.

Thermosetting and Thermoplastic Polymers:

Answer: (C) CCl₂F₂

Explanation: The compound used in refrigeration here is dichlorodifluoromethane (CCl₂F₂), also known as Freon-12 or R-12, a chlorofluorocarbon (CFC). It is a non-toxic, non-flammable, easily liquefied gas that is chemically stable and has a boiling point of −29.8°C. It absorbs a large amount of heat when it evaporates, which makes it an effective refrigerant. CF₄ is very inert and is not used for refrigeration, CCl₄ is toxic and was used as a solvent and in old fire extinguishers, and COCl₂ (phosgene) is a poisonous war gas. CFCs such as R-12 were later phased out under the Montreal Protocol because they destroy stratospheric ozone.

Halogenated Compounds:

Answer: (A) Acidic

Explanation: Iron(III) chloride is the salt of a strong acid (HCl) and a weak base (Fe(OH)₃). In water it dissociates completely into Fe³⁺ and Cl⁻ ions. The Fe³⁺ ion is small and highly charged, so it hydrolyses water: Fe³⁺ + 3H₂O ⇌ Fe(OH)₃ + 3H⁺. The free H⁺ ions make the solution acidic, with a pH of about 2 to 3 for a typical solution. The Cl⁻ ion comes from a strong acid and does not hydrolyse, so nothing balances the H⁺ produced. The paper’s hint “3FeOCl” does not change the result. The solution is acidic and not amphoteric.

Hydrolysis of Salts: