WBCS Main Environmental Science Questions and Answers (Previous Year Paper)

Answer: (D) Kerala

Explanation: The Silent Valley Movement was a late 1970s campaign in Palakkad district, Kerala, against a proposed hydroelectric project on the Kunthipuzha River. The dam would have flooded evergreen rainforest that shelters the endangered lion-tailed macaque. Public and scientific pressure led to the project being dropped, and the area became a national park in 1984.

Environmental Movements of India:

Answer: (C) Sewage

Explanation: Biochemical Oxygen Demand (BOD) is the amount of oxygen microorganisms use to break down organic matter in water. Sewage is rich in biodegradable organic matter, so more sewage means more microbial decomposition and a higher BOD. This lowers dissolved oxygen and harms aquatic life.

BOD Details:

Answer: (B) 1972

Explanation: The National Committee on Environmental Planning and Coordination (NCEPC) was set up in 1972, soon after the Stockholm Conference, to advise the government on environmental planning. It was the first national-level environmental body in India. In 1985 it was replaced by the Ministry of Environment and Forests.

Environmental Institutions and Laws of India:

Answer: (D) Panna

Explanation: Among the given options, Panna (Madhya Pradesh) is the most recently notified biosphere reserve, declared in 2011. Nilgiri (1986) and Gulf of Mannar (1989) are much older. Panna was added to UNESCO’s World Network of Biosphere Reserves in 2020. Note that “Andaman and Nicobar” is not an official reserve name; the official one is Great Nicobar (1989).

Biosphere Reserves of India (18 in total):

Key Facts

Answer: (C) 17

Explanation: The UN Sustainable Development Goals (SDGs) are 17 interlinked goals adopted by all UN member states in September 2015 under the 2030 Agenda for Sustainable Development. They replaced the 8 Millennium Development Goals (2000-2015). The goals have 169 targets and a deadline of 2030.

SDG Details:

Answer: (B) Eye irritation

Explanation: PAN (Peroxyacetyl Nitrate) is a secondary pollutant formed when nitrogen oxides and hydrocarbons react in sunlight. It is a strong lachrymator, so its main effect on humans is eye irritation, along with breathing discomfort. It also damages plants by harming leaf tissue. It is not a known cause of skin or liver cancer.

PAN Details:

Answer: (B) Lotic

Explanation: A lotic ecosystem is one with flowing water, such as rivers, streams and springs. The continuous current keeps the water well oxygenated and carries nutrients and organisms downstream. Standing water bodies like lakes and ponds are called lentic ecosystems.

Aquatic Ecosystem Terms:

Answer: (D) 16.8 Km

Explanation:

• Variation by Latitude: The height of the troposphere is not uniform across the globe. It varies significantly based on latitude and temperature:
  Equator: 16 to 18 km (highest due to intense solar heating and strong convective currents).
  Mid-latitudes: 10 to 12 km.
  Poles: 8 to 9 km (lowest due to cold air contracting).
• Maximum Height: Since the layer pushes the highest near the equator, the maximum height reachable from the Earth’s surface aligns with the upper equatorial limit, which is 16.8 km in this specific context.

Answer: (D) 74%

Explanation: Coal-based thermal plants are the backbone of India’s electricity supply. Coal supplies roughly three-fourths of the electricity generated in India, which matches the 74% option. The exact share shifts slightly each year as solar, wind and hydro grow. Note that the question asks about the share of electricity generated, not installed capacity, which is lower (about 50%).

Power Generation in India:

Answer: (A) SO₂

Explanation: Lichens absorb water and nutrients directly from the air through their surface, with no protective cuticle or roots. Sulphur dioxide damages their chlorophyll and disrupts the algal partner, so lichens disappear first in SO₂-polluted areas. This makes them reliable bioindicators of air quality.

Lichen as a Bioindicator:

Answer: (B) Lindemann

Explanation: The 10% law of energy transfer was proposed by Raymond Lindeman in 1942. It states that only about 10% of the energy at one trophic level is passed on to the next, while the rest is lost mainly as heat through respiration and metabolism. This is why food chains are short, usually limited to 4-5 trophic levels.

Ecology Concepts and Scientists:

Answer: (A) Anthracite

Explanation: Anthracite is the highest rank of coal, with about 90-98% carbon, very low moisture and volatile matter, and the highest calorific value. It burns with a short blue flame and almost no smoke. Peat and lignite are lower in rank, and bituminous coal sits in between.

Types of Coal:

Answer: (C) bioremediation

Explanation: Bioremediation is the use of living microorganisms such as bacteria and fungi to break down or detoxify pollutants in soil, water and air. The microbes use the pollutants as a source of food or energy and convert them into harmless products like carbon dioxide, water and biomass. The terms microremediation and nanoremediation are not standard names for this process.

Bioremediation:

Answer: (C) Both

Explanation: Both potassium permanganate (KMnO₄) and chlorine (Cl₂) are strong oxidising agents that kill disease-causing microorganisms in water. Chlorine is the most widely used disinfectant in municipal supplies, while KMnO₄ is commonly used for disinfecting wells and ponds in rural areas. NO₂ is an air pollutant, not a water disinfectant.

Water Disinfection Methods:

Answer: (C) Industry

Explanation: Industry is the largest consumer of commercial energy in India, using roughly half of the total, mainly coal, electricity and petroleum products. Steel, cement, fertilizer, chemicals and textiles are the major energy-intensive industries. Transport comes next, followed by the household and agriculture sectors.

Energy Use in India:

Answer: (C) Asphalt

Explanation: Albedo is the fraction of incoming solar radiation reflected by a surface. Asphalt is dark and absorbs most sunlight, reflecting only about 4-12%, which is the lowest among the options. Fresh snow reflects up to 80-90%, soil about 10-20%, and forest about 8-18%. Low albedo surfaces heat up quickly, which adds to the urban heat island effect.

Albedo of Different Surfaces:

Answer: (B) Gause

Explanation: The Competitive Exclusion Principle, also called Gause’s Principle, states that two species competing for the same limited resource cannot coexist indefinitely in the same habitat. One will outcompete the other, leading to its local extinction or a shift in its niche. G.F. Gause demonstrated this in 1934 using experiments with two Paramecium species.

Competition and Niche Concepts:

Answer: (C) Urn-shaped

Explanation: A diminishing (declining) age pyramid has a narrow base and a wider middle, giving an urn or bell-like shape with a tapering bottom. It shows a population with a low birth rate, fewer young individuals than middle-aged ones, and a shrinking future population. Countries such as Japan and Germany show this pattern.

Age Pyramid Types:

Answer: (A) Haeckel

Explanation: The term “Oekologie” (ecology) was coined in 1866 by the German biologist Ernst Haeckel. It comes from the Greek words “oikos” (house or habitat) and “logos” (study), meaning the study of organisms in their home environment. Haeckel was a follower of Darwin and defined ecology as the study of the relationships between organisms and their surroundings.

Ecology Terms and Founders:

Answer: (C) Mesosphere

Explanation: The mesosphere extends from about 50 km to 80-85 km above the surface. Temperature falls with height in this layer, reaching about -90°C at the mesopause, the lowest temperature found anywhere in the atmosphere. Meteors burn up here as they enter the atmosphere.

Atmospheric Layers:

Answer: (A) Outdoor Air Pollution

Explanation: An Electrostatic Precipitator (ESP) removes fine particulate matter such as fly ash and dust from industrial exhaust gases. It charges the particles with a high-voltage corona discharge and collects them on oppositely charged plates. ESPs are installed in the chimneys of thermal power plants, cement kilns and steel plants, so they control outdoor (ambient) air pollution at the source.

Air Pollution Control Devices:

Answer: (D) SF₆

Explanation: Global Warming Potential (GWP) compares how much heat a gas traps relative to CO₂ over a set period, usually 100 years. Sulphur hexafluoride (SF₆) has a GWP of about 23,500 to 25,200 times that of CO₂ and stays in the atmosphere for around 3,200 years, making it the most potent among the options. CFCs are also very high (thousands of times CO₂), but lower than SF₆.

Global Warming Potential of Gases (100-year basis):

Answer: (D) Radioactive elements

Explanation: The International Atomic Energy Agency (IAEA) is the UN-affiliated body that promotes the safe and peaceful use of nuclear energy. It sets safety standards for nuclear facilities, radioactive waste management and radiation protection, and monitors nuclear materials through safeguards. It was established in 1957 and is headquartered in Vienna, Austria.

Radiation and Nuclear Safety:

Answer: (C) Coliform

Explanation: Coliform bacteria live in the intestines of humans and warm-blooded animals, so their presence in water signals faecal contamination and possible disease-causing organisms. Because testing for every pathogen is difficult, water purity is judged by the absence of coliforms, especially E. coli. Safe drinking water should show zero coliforms per 100 mL.

Water Quality Indicators:

Answer: (D) Thermosphere

Explanation: The thermosphere lies above the mesosphere, from about 80-85 km to roughly 500 km. Its air is extremely thin, but it absorbs high-energy X-rays and ultraviolet radiation from the Sun, so temperature rises sharply with height, reaching 1500°C or more. It contains the ionosphere, where auroras occur and radio waves are reflected.

Thermosphere:

Answer: (B) Tobacco

Explanation: The first transgenic plants were produced in 1983 using tobacco. Scientists introduced an antibiotic resistance gene into tobacco cells with the help of Agrobacterium tumefaciens, and whole plants were regenerated from them. Tobacco was chosen because it is easy to transform and regenerate in tissue culture.

Transgenic Plants:

Answer: (B) Mercury

Explanation: Minamata disease is a neurological disorder caused by mercury poisoning, specifically methylmercury. It was first identified in 1956 in Minamata, Japan, where a chemical factory (Chisso Corporation) discharged mercury-laden waste into the bay. The mercury was converted to methylmercury by bacteria, accumulated in fish and shellfish through biomagnification, and poisoned people who ate them.

Heavy Metal Diseases:

Answer: (B) 18

Explanation: India had 18 notified biosphere reserves in 2023, with Panna (2011) being the most recent addition. Of these, 12 are included in UNESCO’s World Network of Biosphere Reserves. Note that the number can change over time, so this answer reflects the position at the time of the exam.

Biosphere Reserves of India:

Answer: (A) 1

Explanation: Global Warming Potential (GWP) is measured relative to carbon dioxide, which is the reference gas. CO₂ is therefore assigned a GWP of exactly 1 over any time period, and the GWP of every other greenhouse gas is expressed as a multiple of this value.

GWP Details:

Answer: (D) 60%

Explanation: Biogas (gobar gas) produced from cow dung by anaerobic digestion contains about 55-65% methane, so 60% is the best match among the options. The remaining gas is mostly carbon dioxide (30-40%) with traces of hydrogen sulphide, hydrogen and water vapour. Methane is the combustible component that makes biogas a useful fuel.

Biogas (Gobar Gas):

Answer: (C) 5

Explanation: According to the geographical and climate-based classification used by the Government of India (and detailed in NCERT textbooks), the natural vegetation of India is broadly divided into 5 major forest groups:
1. Mangrove Forests (Littoral/Swamp forests)
2. Tropical Evergreen Forests (Rainforests)
3. Tropical Deciduous Forests (Monsoon forests—the most widespread in India)
4. Tropical Thorn Forests and Scrubs
5. Montane Forests (Mountain vegetation)

Answer: (B) 15°C

Explanation: Earth reflects about 30% of incoming solar radiation back to space (its albedo). Together with the natural greenhouse effect, this gives a global average surface temperature of about 15°C. Without the greenhouse effect, Earth’s average temperature would be about -18°C, which is too cold to support life as we know it.

Earth’s Temperature and Energy Balance:

Answer: (C) Acid Rain

Explanation: Stone cancer is the slow corrosion of marble and limestone monuments. Acid rain, formed when SO₂ and NOx dissolve in rainwater to make sulphuric and nitric acids, reacts with calcium carbonate in the stone and converts it into soluble calcium sulphate. The surface then flakes and crumbles. The Taj Mahal in Agra is a well-known example, affected by emissions from the nearby Mathura refinery and industries.

Stone Cancer and Acid Rain:

Answer: (B) Carbon dioxide

Explanation: Carbon dioxide is a natural component of the atmosphere, essential for photosynthesis, and is not harmful at normal levels, so it is not normally treated as a pollutant. It becomes an environmental concern only when excess amounts enhance the greenhouse effect. Hydrocarbons, carbon monoxide and sulphur dioxide are harmful to health even at low concentrations and are classed as air pollutants.

Common Air Pollutants:

Answer: (C) Phthalate

Explanation: Phthalates are synthetic chemicals, not elements. They are esters of phthalic acid, used to make plastics such as PVC soft and flexible, and they act as endocrine disruptors. Lead, radon and mercury are naturally occurring elements found in the Earth’s crust and are hazardous to human health.

Hazardous Substances:

Answer: (B) Depletion of ozone layer

Explanation: The stratospheric ozone layer absorbs most of the Sun’s harmful UV-B radiation. When it thins, more UV-B reaches the Earth’s surface, which increases sunburn, premature skin ageing and skin cancers such as melanoma. It also causes cataracts and weakens the immune system.

Ozone Depletion and UV Effects:

Answer: (A) ecology

Explanation: Ecology is the scientific study of the interactions between living organisms and their physical and biological environment. The term was coined by Ernst Haeckel in 1866. An ecosystem is the functional unit where these interactions occur, not the study itself. Phytogeography studies plant distribution, and ethology studies animal behaviour.

Ecology and Related Branches:

Answer: (D) Water pollution

Explanation: Cultural eutrophication is the accelerated enrichment of a water body with nutrients, mainly nitrates and phosphates, caused by human activities such as sewage discharge, detergents and fertiliser runoff. The excess nutrients trigger algal blooms. When the algae die, their decomposition uses up dissolved oxygen, harming fish and other aquatic life.

Eutrophication:

Answer: (B) Lower the nutrient levels

Explanation: Dead zones form when excess nutrients cause algal blooms, and the decomposition of dead algae then uses up dissolved oxygen. Lowering nutrient levels (nitrogen and phosphorus) tackles the root cause by stopping the bloom cycle before oxygen is depleted. Adding oxygen only treats the symptom, while more algae or more decomposing bacteria would worsen the oxygen loss.

Dead Zones and Nutrient Control:

Answer: (C) Logging a forest

Explanation: Anthropogenic means caused or produced by human activity. Logging a forest is a direct human action. Water backing up behind a beaver dam, dinosaurs going extinct and a mudslide burying a stream are all natural events not caused by humans.

Anthropogenic vs Natural Causes:

Answer: (D) Composting

Explanation: Composting is the biological decomposition of organic waste by microorganisms into humus-rich manure. It recycles nutrients to the soil, reduces the volume of waste going to landfills, produces no toxic fumes and needs little energy, so it is the most eco-friendly option. Landfills cause leachate and methane emissions, while incineration and pyrolysis release gases and need high energy.

Solid Waste Disposal Methods:

Answer: (D) All of the above

Explanation: Spread of insect-borne diseases such as malaria, rising sea levels and higher global air and ocean temperatures are all predicted consequences of climate change. Since options A, B and C are all expected outcomes, none of them is “not a predicted consequence”, so the correct choice is “All of the above” (the question is framed as a negative statement).

Climate Change:

Answer: (B) Montreal Protocol

Explanation: The Montreal Protocol (1987) is the international treaty that controls and phases out the production and use of ozone depleting substances such as CFCs, halons and carbon tetrachloride. It came into force in 1989 and is considered the most successful environmental treaty, with universal ratification. The Kyoto Protocol deals with greenhouse gas reduction, and the Nagoya Protocol deals with access and benefit sharing of genetic resources.

International Environmental Agreements:

Answer: (A) Atmospheric CO2 dissolving in ocean water.

Explanation: The oceans absorb about 25-30% of the CO₂ released by human activities. When CO₂ dissolves in seawater it forms carbonic acid, which releases hydrogen ions and lowers the pH. This also reduces carbonate ions, which corals, molluscs and other shell-forming organisms need to build their shells and skeletons.

Ocean Acidification:

Answer: (B) Sewage and agricultural fertilizers

Explanation: Phosphates enter water bodies mainly from domestic sewage (human waste and phosphate-based detergents) and from agricultural runoff carrying phosphate fertilizers. Phosphate rock is only the raw material for fertilizers and detergents, and it is not a significant direct source of pollution. Excess phosphate drives eutrophication and algal blooms.

Phosphate Pollution:

Answer: (A) PAN

Explanation: A secondary pollutant is not emitted directly but forms in the atmosphere through reactions between primary pollutants. PAN (Peroxyacetyl Nitrate) forms when nitrogen oxides and hydrocarbons react in sunlight. Aerosols, CO and CO₂ can be released directly from sources, so they are treated as primary pollutants (aerosols can be both, but PAN is the clear secondary pollutant).

Primary vs Secondary Pollutants:

Answer: (C) World Meteorological Organisation

Explanation: The State of the Global Climate report is the annual flagship publication of the World Meteorological Organization (WMO), a specialised agency of the UN. The 2021 edition, released in May 2022, reported record-high greenhouse gas concentrations, rising sea levels and ocean heat, and the seventh-warmest year on record at about 1.11°C above the pre-industrial average.

Climate Reports and Organisations:

Answer: (A) Heterotrophic

Explanation: Bacteria that feed on decaying organic matter cannot make their own food, so they depend on ready-made organic compounds. This makes them heterotrophic, and more specifically saprotrophic decomposers. Autotrophic organisms make their own food through photosynthesis or chemosynthesis. Fungi and cyanobacteria are groups of organisms, not descriptions of a mode of nutrition.

Modes of Nutrition:

Answer: (B) National Parks

Explanation: National Parks have the strictest protection among these categories. Under the Wildlife (Protection) Act 1972, no human activity such as grazing, hunting, cultivation or collection of forest produce is permitted inside them, and no rights are allowed. In Wildlife Sanctuaries, some activities and local rights may be permitted, and Biosphere Reserves and Ramsar wetlands allow regulated use in their buffer or wise-use zones.

Protected Areas of India:

Answer: (B) 0.05°C

Explanation: Global average temperature has risen by about 1.1-1.2°C since pre-industrial times. Recent decades show a warming rate of roughly 0.18-0.2°C per decade, which works out to about 0.02°C per year. Among the options, 0.05°C per year is the closest and is the accepted answer for this question. The options 0.5°C and 1°C per year are far too high.

Global Warming Rates:

Answer: (A) Desalination

Explanation: Desalination removes dissolved salts from seawater or brackish water to make it fit for drinking. It is the standard solution where no freshwater source exists, especially in coastal and arid regions. Groundwater mining only depletes existing aquifers, while sublimation and transpiration are natural phase-change and plant processes that do not supply drinking water.

Desalination:

Answer: (C) 37°C

Explanation: Sludge digestion is the anaerobic breakdown of sewage sludge by bacteria, producing biogas rich in methane. Mesophilic digestion, which works best at about 35-37°C, is the most common and stable form, so 37°C is the optimum among the options. Temperatures far below this slow the bacteria, and very high temperatures need special thermophilic bacteria.

Sludge Digestion:

Answer: (D) rabbits

Explanation:

• Cause of Minamata Disease: Minamata disease is a severe neurological syndrome caused by methylmercury poisoning. In the 1950s, a chemical plant in Minamata, Japan, discharged industrial wastewater containing high concentrations of methylmercury into the bay.
• Biomagnification via Food Chain: The methylmercury accumulated in marine life and entered the local food web, multiplying in concentration at each trophic level (biomagnification).
• Affected Animals: Animals that shared the fish-heavy diet of the local fishermen—such as cats (famously known for developing “dancing cat disease”), dogs, and pigs—ate the contaminated seafood or leftovers and suffered severe mercury toxicity.
• Why Rabbits Remained Free: Rabbits are strictly herbivores. Because they subsist entirely on terrestrial vegetation rather than marine life or fish-based scraps, they were completely bypassed by the aquatic biomagnification pathway and remained free from the disease.

Answer: (B) Biogeography

Explanation: Biogeography is the study of how species and ecosystems are distributed across geographic space and through geological time. It explains why particular organisms live in particular regions, using factors such as climate, continental drift, dispersal barriers and evolutionary history. Alfred Russel Wallace is regarded as the father of biogeography.

Biogeography:

Answer: (C) Denitrification

Explanation: Denitrification is the microbial conversion of nitrate (NO₃⁻) into nitrogen gas (N₂) under anaerobic conditions, which returns nitrogen to the atmosphere. Denitrifying bacteria such as Pseudomonas and Thiobacillus carry it out. Nitrification converts ammonia to nitrate, nitrogen fixation converts N₂ into ammonia, and assimilation is the uptake of nitrogen by plants.

Nitrogen Cycle Processes:

Answer: (B) Presence of prominent polar front and stratospheric clouds; and inflow of CFCs.

Explanation: During the Antarctic winter, a strong polar vortex isolates the air over the continent and temperatures drop below -78°C, forming polar stratospheric clouds (PSCs). Reactions on the surface of these cloud particles convert inactive chlorine from CFCs into active forms. When sunlight returns in spring, the chlorine destroys ozone rapidly and creates the ozone hole.

Antarctic Ozone Hole:

Answer: (A) Tuna (tertiary consumer)

Explanation: Biomagnification is the increase in concentration of persistent toxins such as mercury and DDT at each higher trophic level, because these substances are not broken down or excreted. Tuna is a tertiary consumer at the top of the food chain among the options, so it carries the highest toxin load. Seaweed, a producer, carries the least.

Biomagnification:

Answer: (B) Botanical Garden

Explanation: In-situ conservation protects species in their natural habitats, such as national parks, wildlife sanctuaries and biosphere reserves. A botanical garden keeps plants outside their natural habitat in a managed setting, so it is an ex-situ method of conservation.

In-situ vs Ex-situ Conservation:

Answer: (A) Western Ghats

Explanation: A biodiversity hotspot is a region with very high species richness and endemism that has lost at least 70% of its original vegetation. The Western Ghats (with Sri Lanka) is one of the hotspots found in India. Nanda Devi is a biosphere reserve, while the Eastern Ghats and Aravalli are not hotspots.

Biodiversity Hotspots of India:

Answer: (C) Minimal tillage

Explanation: Biological control, intercropping, minimal tillage and integrated pest management are all practices of sustainable agriculture. Conventional agriculture relies on intensive tillage, chemical pesticides, synthetic fertilisers and monoculture. Since the question’s options are all sustainable practices, it is flawed. If one must be picked, minimal tillage is the option most often cited in answer keys, but intensive tillage is what is truly conventional. Treat this as a doubtful question.

Conventional vs Sustainable Agriculture:

Answer: (A) Nuclear

Explanation: Nuclear energy is derived from uranium and thorium, which are finite minerals that get used up, so it is classed as a non-renewable source. Wind, solar and hydropower are renewable because they are replenished naturally and continuously by the Sun and the water cycle.

Renewable vs Non-Renewable Energy:

Answer: (A) Biomass

Explanation: Biomass, such as wood, crop residue, animal dung and organic waste, is renewable because plants regrow and waste is continually produced. Coal, petroleum and kerosene are fossil fuels that took millions of years to form and are being used up much faster than they are replenished.

Biomass Energy:

Answer: (A) Paling of coral color or decline in zooxanthellae due to climate change

Explanation: Coral bleaching is the loss of colour in corals when they expel the symbiotic algae (zooxanthellae) living in their tissues. These algae give corals their colour and supply most of their food through photosynthesis. Rising sea temperature is the main trigger, and bleached corals turn white and may die if the stress continues. Sea trade and fishing are not the meaning of the term.

Coral Bleaching:

Answer: (A) excess NO2 and SO2 from burning fossil fuels

Explanation: Burning fossil fuels releases sulphur dioxide and nitrogen oxides. These gases react with water vapour, oxygen and other chemicals in the atmosphere to form sulphuric acid and nitric acid, which fall as acid rain with a pH below 5.6. Carbon dioxide only lowers rain pH slightly (to about 5.6), and CO and NH3 are not the main causes.

Acid Rain:

Answer: (D) ozone

Explanation: In the lower atmosphere, UV radiation splits nitrogen dioxide (NO₂) into nitric oxide and a free oxygen atom. This oxygen atom combines with O₂ to form ozone (O₃). Ground-level ozone is therefore a secondary pollutant and a key component of photochemical smog.

Photochemical Reactions:

Answer: (C) Environmental equity

Explanation: Environmental equity is the fair and equal distribution of the Earth’s resources and of environmental benefits and burdens among all people, regardless of race, income or nationality. It is about fairness in sharing. Environmental justice is related but focuses on fair treatment and involvement of all people in making and enforcing environmental laws. Sustainability is meeting present needs without harming future generations, and an ecological footprint measures resource use.

Environmental Equity and Related Concepts:

Answer: (A) CFC

Explanation: Chlorofluorocarbons (CFCs) are stable in the lower atmosphere and drift up into the stratosphere. There, UV radiation breaks them down and releases chlorine atoms, which destroy ozone molecules in a chain reaction. A single chlorine atom can destroy thousands of ozone molecules. DDT and PCBs are persistent organic pollutants, and O₃ is ozone itself.

Ozone Depleting Substances:

Answer: (D) Zoonotic diseases

Explanation: The major causes of biodiversity loss are often summarised as the “Evil Quartet”: habitat loss and fragmentation, overexploitation, invasive alien species, and co-extinction, with climate change now added as a major driver. Zoonotic diseases are infections that pass from animals to humans. They are a human health concern and are not counted among the main drivers of biodiversity loss.

Causes of Biodiversity Loss:

Answer: (C) Poly Vinyl Chloride

Explanation: PVC is Polyvinyl Chloride, a thermoplastic polymer made by polymerising vinyl chloride monomer (CH₂=CHCl). It is strong, durable and cheap, and is widely used in pipes, cables, flooring and packaging. Burning PVC releases toxic hydrogen chloride gas and dioxins, which makes it an environmental concern.

Common Plastics:

Answer: (D) Many suspended solids have been removed

Explanation: Primary treatment is a physical process involving screening, grit removal and sedimentation. It removes settleable and suspended solids and floating material, and reduces BOD by about 30-35%. It does not remove dissolved solids or kill harmful bacteria, so the water is still not potable.

Sewage Treatment Stages:

Answer: (A) reacts with hemoglobin

Explanation: Carbon monoxide binds to haemoglobin in red blood cells about 200-250 times more strongly than oxygen does, forming carboxyhaemoglobin. This reduces the oxygen-carrying capacity of the blood and starves tissues of oxygen, causing headache, dizziness, unconsciousness and, at high levels, death.

Carbon Monoxide:

Answer: (D) the infrared part of the solar radiation.

Explanation: Carbon dioxide is transparent to incoming short-wave solar radiation but absorbs the long-wave infrared (heat) radiation that the Earth’s surface emits. It then re-radiates part of this heat back toward the surface, which warms the lower atmosphere. This is the greenhouse effect, and more CO₂ strengthens it.

Greenhouse Effect:

Answer: (B) O3 layer

Explanation: Supersonic jets fly in the lower stratosphere, where the ozone layer lies. Their exhaust releases nitrogen oxides (NO and NO₂) directly at that height, and these gases destroy ozone molecules through catalytic reactions. The result is thinning of the ozone layer and more UV-B reaching the ground.

Aircraft Emissions and Ozone:

Answer: (C) Larva of stone fly

Explanation: Stone fly larvae are clean-water indicator organisms. They need water that is cold, fast-flowing and rich in dissolved oxygen, so they disappear when organic pollution lowers oxygen levels. Hydrilla, water hyacinth and blue-green algae tolerate or even thrive in polluted, nutrient-rich water.

Indicator Organisms of Water Quality:

Answer: (C) E.coli

Explanation: Escherichia coli lives in the intestines of humans and warm-blooded animals, so its presence in water shows recent faecal contamination and the possible presence of disease-causing organisms. It is easy to detect and does not normally multiply outside the gut, which makes it the standard indicator of polluted water. Vibrio cholerae, Entamoeba histolytica and Salmonella typhi are pathogens, not routine indicators.

Indicator Organisms and Water Testing:

Answer: (B) detritus food chain

Explanation: In the detritus food chain, the energy source is dead organic matter (detritus) such as fallen leaves, dead plants and animal remains, which are originally formed by primary producers. Decomposers like bacteria and fungi break this material down, and detritivores such as earthworms and millipedes feed on it. In terrestrial ecosystems and in many aquatic ones, most of the energy flows through this chain rather than the grazing chain.

Food Chain Types:

Answer: (D) 5.5–6.5

Explanation:

• Nutrient Availability: Essential plant nutrients and minerals (like nitrogen, phosphorus, and potassium) are highly soluble and most readily available for absorption by plant roots in slightly acidic soils.
• Microbial Activity: Beneficial soil microorganisms and nitrogen-fixing bacteria function at their peak performance within this slightly acidic sweet spot.
• Prevention of Toxicity: Keeping the pH above 5.5 prevents toxic accumulations of elements like aluminum and manganese, which can stunt plant growth.

While most cultivated soils globally can span anywhere from 4.5 to 8.5, the specific optimum window targeted for the vast majority of agricultural crops is slightly acidic, making 5.5–6.5 the correct textbook choice for general cultivation.

Answer: (D) Granulated slag

Explanation: Slag is the main solid waste of iron and steel plants. It forms when limestone (flux) combines with impurities in iron ore during smelting in the blast furnace. When molten slag is rapidly cooled with water it becomes granulated slag, which is widely reused in cement and road construction. Red mud comes from aluminium (bauxite) processing, and fly ash and bottom ash come from coal-based thermal power plants.

Industrial Solid Wastes:

Answer: (D) fluorocarbon

Explanation: The official key for this question gives fluorocarbon as the aerosol pollutant linked with jet and supersonic aircraft emissions. Fluorocarbons (CFC-type compounds) are classic aerosol propellant chemicals that damage the ozone layer. Strictly speaking, the main actual exhaust emissions of jets are CO₂, water vapour, NOx and soot, so treat this as an exam-specific answer.

Aircraft Emissions and Aerosols:

Answer: (C) lead

Explanation: Lead was added to petrol as tetraethyl lead (an anti-knock agent), so it was released from vehicle exhausts as fine particles. Lead is a cumulative poison that damages the nervous system, kidneys and blood formation, and it lowers IQ in children. Leaded petrol has been phased out in India since 2000, but lead remains the classic answer for this question.

Lead Pollution:

Answer: (A) Arunachal Pradesh

Explanation: Pakhui (also called Pakke) Wildlife Sanctuary lies in the East Kameng district of Arunachal Pradesh, in the eastern Himalayan foothills. It is bordered by the Kameng and Pakke rivers and is known for its rich birdlife, including four species of hornbill, and for being a tiger reserve. It is also an Important Bird Area.

Pakhui Wildlife Sanctuary:

Answer: (A) methyl isocyanate

Explanation: The Bhopal gas tragedy occurred on the night of 2-3 December 1984 at the Union Carbide pesticide plant, when water entered a storage tank and caused a runaway reaction that released methyl isocyanate (MIC) gas. MIC is highly toxic and irritates the eyes and lungs, causing thousands of deaths and long-term illness. The other options are not the gas involved.

Bhopal Gas Tragedy:

Answer: (B) protein

Explanation: Proteins are the main nitrogen-containing organic compounds in sewage, coming from human waste, food residue and dead organisms. When microorganisms decompose proteins, the nitrogen is released first as ammonia (ammonification). It is then oxidised to nitrite and nitrate. Carbohydrates and fats contain only carbon, hydrogen and oxygen, so they do not add nitrogen.

Nitrogen in Waste Water:

Answer: (A) NO2, O3 and peroxyacetyl nitrate in the presence of sunlight

Explanation: Photochemical smog forms when nitrogen oxides and volatile organic compounds from vehicle exhaust react in strong sunlight. The reactions produce ozone, PAN and aldehydes, which together make up the brownish, irritating haze. Sunlight is essential, so options mentioning only CO, or reactions at low temperature or in the evening, are incorrect.

Photochemical Smog:

Answer: (B) A large number of endemic species

Explanation: A biodiversity hotspot is defined by two criteria: it must contain at least 1,500 species of endemic vascular plants (species found nowhere else), and it must have lost at least 70% of its original habitat. High endemism is therefore the defining feature. A hotspot is not defined by endangered species count, by the type of organisms present, or by extremophiles.

Biodiversity Hotspots:

Answer: (C) a non-degradable pollutant

Explanation: DDT (dichlorodiphenyltrichloroethane) is a persistent organic pollutant. Microbes cannot easily break it down, so it stays in soil and water for years. It is fat-soluble, so it accumulates in body tissues and magnifies along the food chain. This led to problems such as thinning of bird eggshells, and it is banned or restricted in most countries.

DDT:

Answer: (C) increase in temperature due to increase in carbon dioxide concentration of atmosphere

Explanation: The greenhouse effect is the warming of the lower atmosphere and surface when gases such as CO₂, methane and water vapour absorb the infrared heat radiated by the Earth and re-emit part of it back downward. Rising CO₂ concentration strengthens this effect and raises temperature, so option C is the best fit among the choices.

Greenhouse Effect:

Answer: (D) The dose that results in a significant response in 50% of subjects

Explanation: The effective dose 50 (ED50) is the dose of a substance that produces a specified effect in 50% of the test population. It measures potency for a desired or measurable response, not death. The dose that kills 50% of subjects is the lethal dose (LD50), which is a different measure.

Dose-Response Terms:

Answer: (D) Minamata disease

Explanation: Minamata disease is a neurological disorder caused by methylmercury poisoning from eating fish and shellfish contaminated by industrial waste. It was first identified in 1956 in Minamata, Japan, where a chemical factory discharged mercury into the bay. Bacteria converted the mercury to methylmercury, which built up in fish through biomagnification. The other options are not diseases linked to mercury.

Mercury Pollution:

Answer: (B) The amount of O2 utilized by microorganisms for decomposition

Explanation: Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen that microorganisms consume while breaking down biodegradable organic matter in water. It is measured over 5 days at 20°C. A higher BOD means more organic pollution and less oxygen left for aquatic life. Oxygen used by all organisms in general is not what BOD measures.

BOD:

Answer: (D) 1972

Explanation: The United Nations Conference on the Human Environment was held in Stockholm, Sweden, from 5 to 16 June 1972. It was the first major international conference on environmental issues. It produced the Stockholm Declaration and led to the creation of UNEP (United Nations Environment Programme). World Environment Day (5 June) commemorates its opening day.

Stockholm Conference and Later Summits:

Answer: (A) It is the difference between the carbon emission allowed and actually emitted carbon

Explanation: A carbon credit is a tradable permit representing the right to emit one tonne of CO₂ (or its equivalent in other greenhouse gases). A country or company that emits less than its allowed limit earns the unused difference as credits, which it can sell to those exceeding their limits. The idea is to make emission cuts financially rewarding. It is not an IMF loan or a loan for stoves.

Carbon Credit:

Answer: (A) over millions of years; algae and plants

Explanation: Fossil fuels form from the buried remains of ancient organisms subjected to heat and pressure over millions of years. Coal comes mainly from land plants in swampy forests, while oil and natural gas come mainly from marine algae and plankton. Dinosaurs contributed very little, and the process takes far longer than hundreds of years, which is why fossil fuels are non-renewable.

Fossil Fuel Formation:

Answer: (A) By forming a stable compound with hemoglobin

Explanation: Carbon monoxide binds to haemoglobin about 200-250 times more strongly than oxygen does, forming a stable compound called carboxyhaemoglobin. This occupies the sites where oxygen would attach, so the blood carries less oxygen to the tissues. It does not destroy haemoglobin or convert oxygen into carbon dioxide.

Carbon Monoxide and Haemoglobin:

Answer: (A) Non dispersive IR spectroscopy

Explanation: Non-dispersive infrared (NDIR) spectroscopy is the standard method for measuring carbon monoxide in exhaust and ambient air. CO absorbs infrared radiation at a characteristic wavelength (about 4.6 micrometres). The instrument measures how much IR is absorbed by the gas sample, which is directly related to the CO concentration, and it works well at low ppm levels.

CO Monitoring Methods:

Answer: (D) less than the present

Explanation: CO₂ is a major greenhouse gas that absorbs the infrared heat radiated by the Earth and re-emits part of it downward. Without it, much more heat would escape to space and the surface would be cooler than at present. Removing CO₂ would also reduce water vapour in the air, which would amplify the cooling.

Role of CO₂ in Earth’s Temperature:

Answer: (C) plankton and nekton

Explanation: The upper, sunlit zone of the sea (the euphotic or photic zone, down to about 200 m) supports both plankton and nekton. Plankton are drifting organisms: phytoplankton make food by photosynthesis, and zooplankton feed on them. Nekton are active swimmers such as fish, squid and marine mammals that live in the same open water. Benthos live on the bottom, not in the upper water.

Marine Life Zones and Organisms:

Answer: (B) Exhaust of automobile

Explanation: Tetraethyl lead (TEL) was added to petrol as an anti-knock agent to raise its octane rating. When the fuel burned, lead was released from vehicle exhausts as fine particles, polluting air, soil and water. Lead is a cumulative poison that damages the nervous system and lowers IQ in children. India phased out leaded petrol completely in 2000.

Tetraethyl Lead:

Answer: (D) Gasoline

Explanation: Biofuels are fuels made from recently living biomass such as plants, vegetable oils and organic waste. Vegetable oil, green diesel and biogas all come from biological sources. Gasoline (petrol) is refined from crude oil, a fossil fuel formed over millions of years, so it is not a biofuel.

Biofuels:

Answer: (B) Silent Valley Movement

Explanation: The Silent Valley Movement in Kerala opposed a hydroelectric dam on the Kunthipuzha River that would have flooded the rainforest home of the endangered lion-tailed macaque. The macaque became the symbol of the campaign. The project was dropped and the area was declared a national park in 1984.

Lion-tailed Macaque and Silent Valley:

Answer: (A) water pollution

Explanation: The activated sludge process is a secondary sewage treatment method. Wastewater is aerated in a tank where microbial flocs (activated sludge) consume dissolved organic matter, and the flocs are then settled out. This cuts BOD by 85-95%, so it reduces water pollution.

Activated Sludge Process:

Answer: (A) highly productive water body rich in nutrient.

Explanation: A eutrophic water body is rich in nutrients, mainly nitrogen and phosphorus. This supports heavy growth of algae and aquatic plants, so productivity is high. Over time, decomposition of the dead biomass lowers dissolved oxygen and can harm fish.

Lake Types by Nutrient Level:

Answer: (C) In-situ conservation

Explanation: In-situ conservation means protecting species in their natural habitat, where they can keep interacting with their environment and evolving. National parks, wildlife sanctuaries, biosphere reserves and sacred groves are examples. Zoos and other off-site methods keep species outside their natural habitat, which is ex-situ conservation.

In-situ vs Ex-situ Conservation:

Answer: (B) Escherichia coli

Explanation: Escherichia coli lives in the intestines of humans and warm-blooded animals, so its presence in water shows faecal contamination and possible disease-causing organisms. It is easy to detect and does not normally multiply outside the gut, which makes it the standard indicator of polluted water. Entamoeba is a pathogen, while Eichhornia (water hyacinth) and Lemna are aquatic plants.

Water Pollution Indicators:

Answer: (B) London smog

Explanation: London smog is a reducing smog formed in cold, humid conditions when smoke and sulphur dioxide from burning coal combine with fog. It was made famous by the Great Smog of London in December 1952, which caused thousands of deaths. Los Angeles smog is photochemical and is caused by vehicle emissions in sunlight.

London Smog vs Los Angeles Smog:

Answer: (B) Respiratory problem

Explanation: Air pollutants such as particulate matter, SO₂, NO₂, ozone and CO are inhaled and irritate or damage the lungs and airways. This leads to asthma, bronchitis, reduced lung function and aggravated heart disease. Global warming is linked mainly to greenhouse gases, and soil erosion has other causes such as deforestation and overgrazing, so the most direct effect among the options is respiratory problems.

Health Effects of Air Pollutants:

Answer: (A) Ocean

Explanation: The ocean covers about 71% of the Earth’s surface and holds roughly 97% of its water, making it the largest ecosystem on the planet. It also provides the largest living space, since its depth supports life from the surface to the deep seafloor. Forests, grasslands and rivers are much smaller in extent.

Major Ecosystems of the World:

Answer: (B) create P. D. between the two electrodes.

Explanation: In a hydrogen-oxygen fuel cell, hydrogen is oxidised at the anode and oxygen is reduced at the cathode. This releases electrons that flow through an external circuit, creating a potential difference (about 1.23 V per cell) that produces electric current. Water is the by-product, and the main purpose of the cell is generating electricity, not heat or pure water.

Hydrogen-Oxygen Fuel Cell:

Answer: (B) many of birds eggs laid, did not hatch.

Explanation: DDT and its breakdown product DDE biomagnify along the food chain and reach very high levels in birds of prey and fish-eating birds. They interfere with calcium metabolism in the female, so she lays eggs with thin, fragile shells that crack or fail to hatch. Bird numbers fall because of poor breeding success, not because birds stop laying.

DDT and Birds:

Answer: (A) Indonesia

Explanation: Indonesia is the world’s largest producer and exporter of palm oil, supplying roughly half of global output. Malaysia is second. Palm oil comes from the fruit of the oil palm (Elaeis guineensis), and its rapid expansion in Southeast Asia has driven deforestation and loss of habitat for orangutans, tigers and elephants.

Palm Oil:

Answer: (B) Decibel

Explanation: Noise is measured with a sound level meter, and the unit of sound intensity level is the decibel (dB). The decibel scale is logarithmic, so every increase of 10 dB means a tenfold rise in sound intensity. Hertz measures frequency, and joule measures energy.

Noise Pollution:

Answer: (D) non-biodegradable pollutant

Explanation: Non-biodegradable pollutants cannot be broken down by microorganisms, so they persist in the environment for a very long time. DDT is a persistent organic pollutant that resists microbial breakdown, and aluminium cans do not decompose naturally. Both can only be removed by recycling or collection, not by natural decay.

Biodegradable vs Non-biodegradable Pollutants:

Answer: (B) Ozone

Explanation: A secondary pollutant is not released directly from a source but forms in the air through reactions between primary pollutants. Ground-level ozone forms when nitrogen oxides and hydrocarbons react in sunlight. Ammonia, carbon monoxide and nitrogen dioxide are emitted directly, so they are treated as primary pollutants.

Secondary Air Pollutants:

Answer: (C) Mist

Explanation: Aerosols are fine solid or liquid particles suspended in air. Mist consists of tiny liquid droplets, so it is the liquid form among the options. Dust, smoke and fume are solid particles: dust comes from mechanical grinding, smoke from incomplete combustion, and fume from condensation of vapours (such as metal fumes).

Aerosol Types:

Answer: (B) accumulation of salts in soil

Explanation: Salinization is the build-up of soluble salts such as sodium, calcium and magnesium chlorides and sulphates in the upper layer of soil. It occurs mainly through poor drainage, over-irrigation in dry regions and rising saline groundwater. High salt levels draw water out of plant roots, stunt growth and reduce crop yield.

Soil Salinization:

Answer: (A) Natural resources

Explanation: Renewable energy comes from natural resources that are replenished continuously, such as sunlight, wind, flowing water, biomass, geothermal heat and tides. These sources do not get used up on a human timescale. Man-made resources are not an energy source in themselves.

Renewable Energy:

Answer: (A) Benzene and Formaldehyde

Explanation: Volatile Organic Compounds (VOCs) are carbon-based chemicals that evaporate easily at room temperature. Benzene and formaldehyde are VOCs classified as human carcinogens: benzene causes leukaemia, and formaldehyde is linked to nasopharyngeal cancer. Iron and cadmium are metals, and pesticides and weedicides are agrochemicals, not defined as VOCs.

VOCs:

Answer: (C) UNESCO

Explanation: The Biosphere Reserve concept was developed by UNESCO under its Man and Biosphere (MAB) Programme, launched in 1971. These reserves are areas of terrestrial or coastal ecosystems that aim to balance conservation of biodiversity with sustainable use by local communities. Each reserve is nominated by its national government but internationally recognised by UNESCO.

Biosphere Reserves:

Answer: (C) Rachel Carson

Explanation: Silent Spring (1962) was written by the American marine biologist Rachel Carson. The book exposed the harmful effects of indiscriminate pesticide use, especially DDT, on birds and the food chain. Its title refers to a spring without birdsong. It sparked public concern that led to the US ban on DDT in 1972 and to the birth of the modern environmental movement.

Silent Spring and Rachel Carson:

Answer: (A) Methyl isocyanate

Explanation: The Bhopal gas tragedy happened on the night of 2-3 December 1984 at the Union Carbide pesticide plant in Bhopal, Madhya Pradesh. Water entered a storage tank and triggered a runaway reaction that released methyl isocyanate (MIC) gas. MIC is extremely toxic to the eyes and lungs and caused thousands of deaths and long-term illness.

Bhopal Gas Tragedy:

Answer: (B) 1992 at Rio de Janeiro

Explanation: The Earth Summit, officially the UN Conference on Environment and Development (UNCED), was held in Rio de Janeiro, Brazil, in June 1992. It was attended by over 170 countries and produced Agenda 21, the Rio Declaration, the Convention on Biological Diversity, the UNFCCC and the Forest Principles. The 1972 conference was held at Stockholm, not Rio.

Earth Summit and Related Conferences:

Answer: (C) Uttar Pradesh

Explanation: The Chipko Movement began in 1973 in the Chamoli district of the Garhwal Himalaya, which was then part of Uttar Pradesh and is now in Uttarakhand. Villagers, led by women, hugged trees to stop commercial logging. Among the given options, Uttar Pradesh is the answer, as Uttarakhand was formed only in 2000.

Chipko Movement:

Answer: (D) Carbon dioxide

Explanation: Burning fossil fuels such as coal, petrol and natural gas oxidises carbon in the fuel and releases carbon dioxide, the largest contributor to human-caused global warming. Methane is a greenhouse gas but comes mainly from paddy fields, cattle and landfills. Carbon monoxide forms in incomplete combustion and is not a direct greenhouse gas, and hydrogen is not a greenhouse gas.

Greenhouse Gases from Fossil Fuels:

Answer: (B) 5th June

Explanation: World Environment Day is observed every year on 5 June. It was established by the UN General Assembly in 1972 on the opening day of the Stockholm Conference, and was first celebrated in 1973. It is the main UN day for encouraging worldwide awareness and action for the environment, and each year has a theme and a host country.

Important Environmental Days:

Answer: (C) Jim Corbett

Explanation: Jim Corbett National Park in Uttarakhand was established in 1936 as Hailey National Park, making it the first national park in India. It was renamed Ramganga National Park in 1954-55 and then Corbett National Park in 1956, in honour of the hunter-turned-conservationist Jim Corbett. It was also the first reserve to come under Project Tiger in 1973.

First National Parks and Related Facts:

Answer: (B) Madhya Pradesh

Explanation: India’s first commercial-scale biomass-based hydrogen plant was announced at Pithampur in Indore district, Madhya Pradesh, by the Indian Oil-led Bio-hydrogen initiative. It converts agricultural residue and other biomass into hydrogen through gasification. The plant supports India’s National Green Hydrogen Mission and its aim to cut dependence on fossil fuels.

Hydrogen Energy: