UPSC Prelims 2025
Environment & Ecology Previous Year Questions (PYQs)

Detailed Explanation:

Correct Answer: ✅ Option 1

Activated carbon is one of the most widely used adsorbents in water and wastewater treatment. Its effectiveness comes from its highly porous structure and enormous surface area, while its low-cost production from carbon-rich wastes makes it an attractive and sustainable pollution-control material.

✅ Statement I is Correct: Activated carbon is extensively used to remove pollutants from industrial effluents and contaminated water through adsorption.

✅ Statement II is Correct: Activated carbon has a very large surface area and strong adsorption capacity, enabling it to capture heavy metals and other pollutants efficiently.

✅ Statement III is Correct: Activated carbon can be produced from agricultural and environmental wastes such as coconut shells, rice husks, sawdust, and other carbon-rich materials.

✅ Statement II explains Statement I: Its large surface area and adsorption capacity make it effective in pollutant removal.

✅ Statement III explains Statement I: Easy and low-cost production from waste materials makes it an attractive and sustainable remediation tool.

Short Notes: Activated Carbon

• Activated carbon is a highly porous carbon material used as an adsorbent.

• It has a surface area that can exceed 1,000 m²/g.

• Used in water purification, air filtration, and wastewater treatment.

• Effective in removing heavy metals, dyes, pesticides, and organic pollutants.

• Common raw materials include coconut shells, wood, coal, and agricultural residues.

• Works mainly through the process of adsorption, not absorption.

• It is widely used in environmental remediation and pollution control.

Detailed Explanation:

Correct Answer: ✅ Option 1 — The Asian Development Bank (ADB)

The Asian Development Bank launched the Nature Solutions Finance Hub for Asia and the Pacific to mobilize investments for nature-based solutions (NbS). The initiative aims to address climate change, biodiversity loss, and ecosystem degradation by supporting projects that use natural systems for environmental resilience.

✅ Option 1 is Correct: ADB launched the Nature Solutions Finance Hub for Asia and the Pacific.

❌ Option 2 is Incorrect: The Asian Infrastructure Investment Bank did not launch this initiative.

❌ Option 3 is Incorrect: The New Development Bank is not associated with this hub.

❌ Option 4 is Incorrect: The International Bank for Reconstruction and Development did not launch the Nature Solutions Finance Hub.

Short Notes: Nature-Based Solutions (NbS)

• Nature-based Solutions use natural ecosystems to address environmental challenges.

• Examples include mangrove restoration, afforestation, wetland conservation, and watershed management.

• NbS help in climate mitigation, climate adaptation, and biodiversity conservation.

• The ADB Nature Solutions Finance Hub focuses on Asia-Pacific countries.

• It aims to mobilize public and private finance for environmental projects.

• Healthy ecosystems provide services such as carbon sequestration, flood control, and water purification.

• NbS are increasingly recognized as cost-effective climate solutions.

Detailed Explanation:

Correct Answer: ✅ Option 3 (All the three)

Many common items contain plastic materials, even when they do not appear to be made of plastic. Cigarette filters, modern eyeglass lenses, and car tyres all contain synthetic polymer-based materials that qualify as plastics or plastic-derived products.

✅ I. Cigarette Butts – Correct: Cigarette filters are primarily made of cellulose acetate, a synthetic plastic polymer.

✅ II. Eyeglass Lenses – Correct: Most modern eyeglass lenses are made from plastics such as polycarbonate or CR-39 resin, rather than glass.

✅ III. Car Tyres – Correct: Tyres contain synthetic rubber and other polymer-based materials derived from petrochemicals, which are forms of plastic.

Short Notes: Plastics in Everyday Life

• Cellulose acetate used in cigarette filters is a type of plastic.

• Most modern eyeglass lenses are made from polycarbonate due to its light weight and impact resistance.

• Car tyres contain both natural rubber and synthetic polymers.

• Synthetic rubber is produced from petroleum-based chemicals.

• Plastic waste can persist in the environment for hundreds of years.

• Cigarette butts are among the most common forms of plastic litter worldwide.

• Microplastics can be generated from the wear and tear of vehicle tyres.

Detailed Explanation:

Correct Answer: ✅ Option 2

The cement industry is a major contributor to global carbon emissions, accounting for roughly 5–8% of global CO₂ emissions. While both limestone and clay are essential raw materials in cement production, the primary source of CO₂ emissions is the calcination of limestone during clinker manufacturing.

✅ Statement I is Correct: Cement manufacturing contributes more than 5% of global CO₂ emissions, mainly due to clinker production and energy consumption.

✅ Statement II is Correct: Silica-bearing clay is mixed with limestone to provide silica, alumina, and iron oxides required for cement production.

✅ Statement III is Correct: During clinker production, limestone (CaCO₃) is heated and converted into lime (CaO), releasing large amounts of CO₂.

❌ Statement II does not explain Statement I: Mixing clay with limestone is a raw-material requirement and is not the direct cause of significant carbon emissions.

✅ Statement III explains Statement I: The conversion of limestone into lime (calcination) releases CO₂ and is the principal reason for high emissions from the cement industry.

Short Notes: Cement Industry and Carbon Emissions

• The cement industry contributes about 5–8% of global CO₂ emissions.

• The main raw materials are limestone and clay.

• Clinker is the intermediate product used to manufacture cement.

• Calcination reaction: CaCO₃ → CaO + CO₂.

• Around 60% of cement emissions come from the calcination process.

• The remaining emissions mainly come from fuel combustion in kilns.

• Low-carbon cement and carbon capture technologies are being developed to reduce emissions.

Detailed Explanation:

Correct Answer: ✅ Option 1

Article 6 of the Paris Agreement provides a framework for international cooperation in achieving climate goals. It covers both market-based approaches (carbon markets) and non-market approaches, making it one of the most discussed and important provisions of the Paris Agreement.

✅ Statement I is Correct: Article 6 is frequently discussed because it establishes mechanisms through which countries can cooperate to achieve their climate commitments.

✅ Statement II is Correct: Article 6 lays down the framework for international carbon markets, including the transfer and trading of carbon credits.

✅ Statement III is Correct: Article 6 also promotes non-market approaches such as technology transfer, capacity building, policy coordination, and sustainable development cooperation.

✅ Statement II explains Statement I: Carbon markets are a major reason why Article 6 receives significant global attention.

✅ Statement III explains Statement I: Non-market cooperation mechanisms are also central to climate negotiations and sustainable development discussions.

Short Notes: Article 6 of the Paris Agreement

• Article 6 focuses on international cooperation to achieve climate targets.

• It allows countries to trade carbon credits through market mechanisms.

• Article 6.2 deals with bilateral and multilateral carbon trading.

• Article 6.4 establishes a UN-supervised global carbon market mechanism.

• Article 6.8 promotes non-market approaches for climate action.

• It aims to reduce the cost of achieving Nationally Determined Contributions (NDCs).

• Proper implementation helps prevent double counting of emission reductions.

Detailed Explanation:

Correct Answer: ✅ Option 3

At COP28, India did not sign the Declaration on Climate and Health. India's concern was not about the objective of climate-resilient healthcare, but about the practical implications of rapid decarbonization in a developing country where ensuring reliable and accessible healthcare remains a priority.

✅ Statement I is Correct: India refrained from signing the COP28 Declaration on Climate and Health.

❌ Statement II is Incorrect: The declaration is voluntary and non-binding. Signing it does not create a legal obligation to decarbonize the health sector.

✅ Statement III is Correct: India expressed concerns that aggressive decarbonization requirements could affect the resilience, accessibility, and reliability of healthcare services, especially in resource-constrained settings.

✅ Statement III explains Statement I: Concerns regarding healthcare resilience and developmental priorities contributed to India's decision not to sign the declaration.

❌ Statement II does not explain Statement I: Since the declaration is not legally binding, this statement is factually incorrect.

Short Notes: COP28 Declaration on Climate and Health

• The declaration was launched at COP28 (Dubai, 2023).

• It highlights the link between climate change and public health.

• The declaration is voluntary and non-binding.

• It encourages countries to build climate-resilient and sustainable health systems.

• More than 120 countries supported the declaration.

• India did not sign due to concerns over healthcare accessibility and developmental priorities.

• Climate change increases risks from heatwaves, diseases, floods, and extreme weather events.

Detailed Explanation:

Answer: Option 4 — II and III

Simple Explanation:

Statement I — Incorrect. It is NOT a crustacean — it's a spider (arachnid), specifically a tarantula. Crustaceans (like crabs/shrimp) are a completely different animal group.

Statement II — Correct. Its habitat is restricted to certain forest areas in India, specifically the Eastern Ghats.

Statement III — Correct. It is arboreal — meaning it lives in trees and tree crevices/hollows, not on the ground.

📝 Short Notes: Peacock Tarantula / Gooty Tarantula

Detailed Explanation:

Statement I — Incorrect. India's per capita CO₂ emissions are around 1.9–2.0 tonnes, NOT less than 0.5 tonnes. The number given is too low and wrong.

Statement II — Correct. India ranks second in the Asia-Pacific region for CO₂ emissions from fuel combustion — after China (which ranks first).

Statement III — Correct. Electricity and heat production (mostly coal-based) is the largest source of CO₂ emissions in India.

Detailed Explanation:

Correct Answer: ✅ Option 2 (II only)

Most people associate oxygen production with forests, but the oceans are actually the largest source of Earth's oxygen. Marine phytoplankton, algae, and photosynthetic bacteria contribute roughly half of the global oxygen production. Also, atmospheric air contains much higher oxygen concentrations than water.

❌ Statement I is Incorrect: Oceans produce more oxygen than rainforests. Marine phytoplankton are responsible for a major share of global oxygen production.

✅ Statement II is Correct: Marine phytoplankton and photosynthetic bacteria produce about 50% of the world's oxygen through photosynthesis.

❌ Statement III is Incorrect: Atmospheric air contains about 21% oxygen, whereas even well-oxygenated water contains only a small amount of dissolved oxygen. Water does not contain several times more oxygen than air.

Short Notes: Oxygen Cycle and Marine Phytoplankton

• Marine phytoplankton produce nearly 50% of Earth's oxygen.

• Phytoplankton are microscopic photosynthetic organisms found in oceans.

• Oceans are the largest contributor to global oxygen production.

• Atmospheric air contains about 21% oxygen.

• Dissolved oxygen in water is usually measured in mg/L, much lower than oxygen concentration in air.

• Photosynthesis converts CO₂ + Water → Glucose + Oxygen.

• Healthy oceans are essential for maintaining Earth's oxygen balance and climate system.

Detailed Explanation:

Correct Answer: ✅ Option 1

A Circular Economy aims to keep products, materials, and resources in use for as long as possible through reuse, repair, recycling, and efficient production. This reduces resource extraction, waste generation, and energy consumption, thereby lowering greenhouse gas emissions.

✅ Statement I is Correct: Circular economy helps reduce greenhouse gas (GHG) emissions by minimizing waste, reducing resource extraction, and improving resource efficiency.

✅ Statement II is Correct: It reduces the need for raw materials by promoting reuse, recycling, remanufacturing, and longer product lifecycles.

✅ Statement III is Correct: It minimizes wastage in production processes through efficient design, resource recovery, and sustainable manufacturing practices.

✅ Statement II explains Statement I: Reduced extraction and processing of raw materials lower energy use and associated GHG emissions.

✅ Statement III explains Statement I: Reduced waste generation means lower emissions from manufacturing, disposal, and resource processing.

Short Notes: Circular Economy

• Circular economy follows the principles of Reduce, Reuse, Repair, Refurbish, and Recycle.

• It aims to keep materials in use for the maximum possible time.

• Reduces dependence on virgin raw materials.

• Helps lower greenhouse gas emissions and environmental degradation.

• Minimizes waste sent to landfills and incinerators.

• Supports resource efficiency and sustainable production.

• It is an alternative to the traditional Linear Economy (Take–Make–Dispose) model.

Detailed Explanation:

Correct Answer: ✅ Option 1 (Silver iodide and Potassium iodide)

Artificial rainfall, also known as cloud seeding, is a weather modification technique used to induce precipitation. It is sometimes employed to reduce severe air pollution by washing pollutants and particulate matter out of the atmosphere.

✅ Option A is Correct: Silver iodide (AgI) and Potassium iodide (KI) are commonly used cloud-seeding agents. Their crystal structure resembles ice, helping water droplets condense and form rain.

❌ Option B is Incorrect: Silver nitrate is not a standard cloud-seeding material.

❌ Option C is Incorrect: Potassium nitrate is not used for inducing rainfall through cloud seeding.

❌ Option D is Incorrect: Neither silver nitrate nor potassium chloride is used as a conventional cloud-seeding agent.

Short Notes: Cloud Seeding

• Cloud seeding is an artificial technique used to enhance rainfall.

• Common seeding agents include silver iodide (AgI), potassium iodide (KI), and dry ice (solid CO₂).

• These substances act as condensation or ice nuclei.

• Cloud seeding is used to reduce air pollution, increase water availability, and mitigate drought.

• It works only when suitable clouds are already present.

• The technique cannot create clouds from a clear sky.

• Several countries, including India, China, UAE, and the USA, have experimented with cloud seeding.

Detailed Explanation:

Correct Answer: ✅ Option 3 (Both I and II)

Wet-bulb temperature combines air temperature and humidity. A wet-bulb temperature of 35°C is considered a critical threshold because the human body can no longer cool itself effectively through sweating. The World Bank has warned that parts of India could face dangerous heat stress conditions due to climate change.

✅ Statement I is Correct: Rising temperatures and climate change are expected to increase the frequency and intensity of floods, tropical cyclones, droughts, and other extreme weather events, particularly affecting Peninsular India.

✅ Statement II is Correct: At a wet-bulb temperature of 35°C, sweat cannot evaporate efficiently. As a result, humans and animals are unable to release body heat, creating life-threatening conditions.

Short Notes: Wet-Bulb Temperature

• Wet-bulb temperature combines heat and humidity into a single measure.

• A wet-bulb temperature of 35°C is considered the upper limit of human survivability for prolonged exposure.

• High humidity reduces the effectiveness of evaporative cooling (sweating).

• Climate change is increasing the frequency of extreme heat events.

• India is considered one of the most vulnerable countries to heat stress.

• Wet-bulb temperature is often used to assess human health risks during heatwaves.

• Heat stress can affect agriculture, labor productivity, livestock, and public health.

Detailed Explanation:

Correct Answer: ✅ Option 1 — The European Union

The European Union enacted the Nature Restoration Law (NRL) to restore degraded ecosystems, enhance biodiversity, and strengthen climate resilience. It is one of the world's most ambitious legally binding nature restoration frameworks.

✅ Option A is Correct: The European Union adopted the Nature Restoration Law (2024) with legally binding restoration targets for ecosystems across member states.

❌ Option B is Incorrect: The World Bank provides financing and technical assistance but does not enact such laws.

❌ Option C is Incorrect: The Organisation for Economic Co-operation and Development offers policy recommendations but does not pass binding environmental legislation.

❌ Option D is Incorrect: The Food and Agriculture Organization supports food security and agriculture but does not enact regional laws like the NRL.

Short Notes: Nature Restoration Law (NRL)

• The Nature Restoration Law was adopted by the European Union in 2024.

• It aims to restore degraded terrestrial, freshwater, coastal, and marine ecosystems.

• The law supports the EU's Biodiversity Strategy 2030.

• It contains legally binding restoration targets for member states.

• Restoration of wetlands, forests, grasslands, rivers, and pollinator habitats is a key focus.

• Healthy ecosystems help in carbon sequestration and climate adaptation.

• The NRL is considered a major step in tackling biodiversity loss and climate change simultaneously.