UPSC IAS / IPS - MCQ Practice Questions

Understanding:

This question is about the ecological and social significance of the Chipko Movement, one of India's most well-known grassroots environmental movements.

Step 1: Origin of Chipko Movement

The Chipko Movement began in 1973 in the Chamoli district of Uttarakhand (then Uttar Pradesh). Local villagers, predominantly women led by figures such as Sundarlal Bahuguna and Gaura Devi, protested against commercial logging by literally hugging (chipko means 'to hug' or 'to stick to') trees to prevent them from being felled.

Step 2: Primary concern

The movement was fundamentally a protest against deforestation and for the conservation of forests. Villagers depended on forests for fodder, fuel, and water, and deforestation was causing soil erosion, floods, and ecological degradation in the Himalayan region.

Step 3: Broader legacy

The movement inspired subsequent forest conservation legislation and contributed to a ban on green felling in the Himalayas. It is globally recognised as a model of community-based environmental activism.

Answer:

The Chipko Movement was primarily associated with the conservation of forests and trees.

Quick Tip:

Chipko = 'to hug' in Hindi. The image of people hugging trees to save them is the defining symbol of this movement. Sundarlal Bahuguna and Gaura Devi are key personalities to remember.

Understanding:

This question tests knowledge of the concept of ecological succession, specifically the properties that define a climax community.

Step 1: What is a climax community?

A climax community is the final, stable stage of ecological succession. It represents the endpoint of successional development in a given climatic region. Examples include tropical rainforests and temperate deciduous forests in appropriate climatic zones.

Step 2: Characteristics of a climax community

Key features include: stability and self-sustainability (organisms can reproduce and maintain the community), high species diversity and biomass, dynamic equilibrium with the local climate, and low net community productivity relative to gross productivity (energy is mainly used in respiration).

Step 3: Identifying the incorrect option

The statement that the climax community is 'continuously changing with new pioneer species replacing existing ones' describes pioneer stages, not the climax stage. Pioneer species appear at the very beginning of succession on bare substrate and are replaced progressively until climax is reached. In a climax community, pioneer species are absent and species composition is relatively stable.

Answer:

A climax community is NOT characterised by continuously changing pioneer species — that is a property of early successional stages.

Quick Tip:

In UPSC questions on succession, remember: pioneer communities are unstable and simple; climax communities are stable, complex, and climatically determined. Net productivity is highest in early succession, not at climax.

Understanding:

This question is about the legal framework for wildlife protection in India under the Wildlife (Protection) Act, 1972, and the significance of its schedules.

Step 1: Structure of schedules under the Act

The Wildlife (Protection) Act, 1972 originally contained six schedules classifying animals and plants based on the degree of protection accorded to them. The 2022 amendment restructured these into four schedules, but the original framework with Schedule I providing the highest protection is the most commonly tested version in UPSC.

Step 2: Schedule I significance

Schedule I animals are accorded absolute protection. Offences against Schedule I species attract the highest penalties under the Act. Species listed include the tiger, lion, elephant, rhinoceros, leopard, snow leopard, clouded leopard, swamp deer, and gharial, among others.

Step 3: Other schedules

Schedule II animals have high protection but slightly lower penalties. Schedules III and IV cover less endangered species with lower levels of protection. Schedule V lists vermin (pests) that can be hunted. Schedule VI protects specified plants.

Answer:

Schedule I of the Wildlife (Protection) Act, 1972 provides the highest degree of protection to wildlife in India.

Quick Tip:

For UPSC, remember the hierarchy: Schedule I > Schedule II > Schedules III & IV. The tiger (Project Tiger, 1973) is a Schedule I species — a frequent exam link.

Understanding:

This question tests awareness of major international environmental conventions and their specific mandates related to biodiversity and wildlife.

Step 1: CITES

CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) is an international agreement between governments that regulates international trade in wild animals and plants to ensure such trade does not threaten the survival of species. It was opened for signature in 1973 and entered into force in 1975. Species are listed under three appendices based on the level of protection required.

Step 2: CBD

The Convention on Biological Diversity (CBD), adopted at the Rio Earth Summit in 1992, focuses on conservation of biological diversity, sustainable use of its components, and fair sharing of benefits from genetic resources. It does not specifically regulate trade in species.

Step 3: Ramsar Convention

The Ramsar Convention (1971) is specifically about the conservation and sustainable use of wetlands. It has no direct mandate over species trade.

Step 4: Bonn Convention

The Bonn Convention (Convention on Migratory Species, CMS, 1979) focuses on the conservation of migratory species and their habitats. It is not a trade regulation instrument.

Answer:

CITES specifically deals with regulating international trade in endangered species of wild fauna and flora.

Quick Tip:

Remember the mnemonic: CITES = Trade, CBD = Diversity, Ramsar = Wetlands, Bonn = Migratory species. These four are perennial favourites in UPSC Prelims.

Understanding:

This question asks for the precise scientific meaning of carbon sequestration, a process important in climate change mitigation strategies.

Step 1: Definition of carbon sequestration

Carbon sequestration refers to the process by which carbon dioxide is removed from the atmosphere and stored in carbon sinks such as forests (via photosynthesis), soils, oceans, and geological formations (e.g., injection into depleted oil and gas reservoirs). It is a key mechanism in reducing atmospheric greenhouse gas concentrations.

Step 2: Natural vs. artificial sequestration

Natural sequestration occurs through forests (terrestrial carbon sinks), oceans (marine carbon sinks), and wetlands (especially peat bogs and mangroves). Artificial or engineered sequestration includes Carbon Capture and Storage (CCS) technologies used in power plants.

Step 3: Relevance to climate policy

Carbon sequestration is central to Nationally Determined Contributions (NDCs) under the Paris Agreement, with countries pledging to enhance forest cover and carbon sinks. India's NDC includes creating an additional carbon sink through forest and tree cover.

Answer:

Carbon sequestration is the long-term storage of carbon in natural or artificial reservoirs, removing it from the atmosphere.

Quick Tip:

Mangroves are among the most efficient carbon sequesterers per unit area — a favourite UPSC fact. They store carbon in both biomass and sediments (termed 'blue carbon').

Understanding:

This question is about the fundamental structure of food chains and the organisation of trophic levels in an ecosystem.

Step 1: Trophic levels defined

A trophic level represents a position in a food chain. Energy flows from one trophic level to the next, with approximately 10% of energy transferred at each step (10% law, proposed by Lindeman).

Step 2: Correct sequence

The standard sequence from the lowest to highest trophic level is:

Decomposers act on all levels but are not part of the linear food chain sequence.

Step 3: Why other options are wrong

Decomposers do not begin the food chain — producers do. Placing tertiary consumers before secondary consumers inverts the flow of energy.

Answer:

The correct sequence from lowest to highest trophic level is: Producers → Primary consumers → Secondary consumers → Tertiary consumers.

Quick Tip:

Remember Lindeman's 10% law: only 10% of energy is transferred from one trophic level to the next. This explains why food chains rarely exceed 4–5 levels.

Understanding:

This question is about the concept of albedo, an important factor in Earth's energy budget and climate change feedbacks.

Step 1: What is albedo?

Albedo is the measure of the reflectivity of a surface. It is expressed as the fraction of incoming solar radiation that is reflected back into space. A high albedo means a surface reflects most sunlight; a low albedo means a surface absorbs most sunlight.

Step 2: Role in climate change

Ice and snow have very high albedo (reflecting up to 80–90% of solar radiation). As global warming melts ice caps and glaciers, darker ocean or land surfaces are exposed. These darker surfaces have lower albedo and absorb more heat, further warming the planet. This is called the ice-albedo positive feedback loop.

Step 3: Distinguishing from other effects

The greenhouse effect involves trapping of outgoing infrared radiation — not reflection. Latent heat release is part of the hydrological cycle. Ocean warming from absorption of sunlight is the opposite of the albedo effect.

Answer:

The albedo effect refers to the reflection of incoming solar radiation back into space by bright surfaces like ice, snow, and clouds.

Quick Tip:

The melting of Arctic sea ice is the classic example of the ice-albedo feedback in UPSC questions: less ice → lower albedo → more absorption → more warming → further melting.

Understanding:

This question tests knowledge of the Kyoto Protocol's specific mechanisms for achieving emission reduction targets in a cost-effective manner.

Step 1: The Kyoto Protocol's flexibility mechanisms

The Kyoto Protocol (1997, entered into force 2005) introduced three market-based mechanisms to help Annex I (developed) countries meet their emission reduction targets at lower cost:

1. Emissions Trading (ET): Allows countries with surplus emission allowances to sell credits to countries that exceed their targets.

2. Clean Development Mechanism (CDM): Allows Annex I countries to implement emission-reduction projects in developing countries and earn Certified Emission Reduction (CER) credits.

3. Joint Implementation (JI): Allows Annex I countries to earn Emission Reduction Units (ERUs) by investing in emission-reduction projects in other Annex I countries.

Step 2: Eliminating other options

The Green Climate Fund and Loss and Damage Fund are associated with the UNFCCC Paris Agreement era, not the Kyoto Protocol. Nationally Determined Contributions and Global Stocktake are Paris Agreement (2015) concepts. Carbon border taxes are a national/regional policy instrument, not a Kyoto mechanism.

Answer:

The Kyoto Protocol's three flexibility mechanisms are Emissions Trading, the Clean Development Mechanism, and Joint Implementation.

Quick Tip:

A useful memory device: Kyoto = CDM + JI + ET. The Paris Agreement (2015) replaced Kyoto's binding targets with voluntary NDCs — a shift frequently tested in UPSC.

Understanding:

This question requires identification of the incorrect statement about mangrove ecosystems in India.

Step 1: Checking each statement

Mangroves as natural buffers: True. Dense mangrove stands significantly reduce wave energy, storm surges, and erosion. The 2004 Indian Ocean tsunami caused less damage in areas with intact mangrove cover.

Step 2: Sundarbans as the largest mangrove

True. The Sundarbans, shared between India (West Bengal) and Bangladesh, is the largest mangrove ecosystem in India and the world. It is a UNESCO World Heritage Site and a Tiger Reserve.

Step 3: Mangroves only on the western coast

False and therefore the incorrect statement. India has mangrove forests on both the eastern and western coastlines. Significant mangrove areas exist on the eastern coast (Sundarbans in West Bengal, Bhitarkanika in Odisha, Coringa in Andhra Pradesh) as well as on the western coast (Goa, Maharashtra, Gujarat). The eastern coast has larger mangrove areas overall.

Step 4: Mangroves as carbon sinks

True. Mangroves store carbon in both above-ground biomass and in waterlogged sediments (blue carbon). They are among the most carbon-dense ecosystems on Earth.

Answer:

The statement that mangroves are found only along the western coastline of India is incorrect.

Quick Tip:

India's total mangrove cover is approximately 4,992 sq km (State of Forest Report 2021). West Bengal has the largest share. Both coasts have mangroves — remember Bhitarkanika (Odisha) on the east.

Understanding:

This question is about eutrophication, an important process in water pollution ecology frequently tested in environmental science.

Step 1: Definition and cause

Eutrophication is the process by which a water body becomes overly enriched with nutrients, particularly nitrogen and phosphorus. These nutrients typically enter water bodies through agricultural runoff (fertilisers), sewage discharge, and industrial effluents.

Step 2: Consequences

The excess nutrients trigger explosive growth of algae and cyanobacteria, forming algal blooms. When these algae die and decompose, aerobic bacteria consume large amounts of dissolved oxygen, creating hypoxic (low oxygen) or anoxic (no oxygen) conditions. This leads to the death of fish and other aquatic organisms — a condition called a 'dead zone'.

Step 3: Distinguishing eutrophication from other processes

Thermal pollution (option A) involves temperature changes, not nutrient enrichment. Heavy metal accumulation (option C) is a separate form of pollution called bioaccumulation or sediment contamination. Salinity changes (option D) describe freshwater intrusion, not nutrient-driven oxygen depletion.

Answer:

Eutrophication is the excessive enrichment of water with nutrients causing algal blooms and oxygen depletion.

Quick Tip:

Eutrophication is linked to the 'dead zones' in seas such as the Arabian Sea dead zone off the west coast of India. Phosphorus is often the key limiting nutrient in freshwater eutrophication, while nitrogen limits marine eutrophication.

Understanding:

This question tests knowledge of India's flagship climate change policy framework, the National Action Plan on Climate Change (NAPCC).

Step 1: Background of NAPCC

The NAPCC was launched on 30 June 2008 by the Prime Minister's Council on Climate Change. It outlines India's strategy for addressing climate change while pursuing national development goals. It operates on a principle of co-benefits — actions that serve both development and climate goals.

Step 2: The eight national missions

The NAPCC consists of eight national missions:

1. National Solar Mission

2. National Mission for Enhanced Energy Efficiency

3. National Mission on Sustainable Habitat

4. National Water Mission

5. National Mission for Sustaining the Himalayan Ecosystem

6. National Mission for a Green India

7. National Mission for Sustainable Agriculture

8. National Mission on Strategic Knowledge for Climate Change

Step 3: Why other options are wrong

The number is specifically 8, not 6, 10, or 12. This is a direct factual recall question.

Answer:

The NAPCC consists of eight national missions.

Quick Tip:

The first and most prominent mission is the National Solar Mission (now part of the International Solar Alliance initiative). Memorise the list of all 8 missions using the acronym: Solar, Energy, Habitat, Water, Himalayan, Green India, Agriculture, Strategic Knowledge.

Understanding:

This question requires accurate matching of Indian biosphere reserves with their correct geographical locations (states).

Step 1: Checking Nanda Devi — Uttarakhand

The Nanda Devi Biosphere Reserve is located in Uttarakhand (formerly Uttar Pradesh). It covers the Nanda Devi National Park and the Valley of Flowers National Park, both UNESCO World Heritage Sites. This pairing is correct.

Step 2: Checking Nokrek — Manipur

Nokrek Biosphere Reserve is located in Meghalaya, not Manipur. It is known for the citrus gene pool and is recognised by UNESCO.

Step 3: Checking Agasthyamalai — Tamil Nadu only

Agasthyamalai Biosphere Reserve spans parts of both Kerala and Tamil Nadu, not Tamil Nadu alone. It is in the Western Ghats and is a UNESCO-recognised biosphere reserve.

Step 4: Checking Simlipal — Jharkhand

Simlipal Biosphere Reserve is located in Odisha, not Jharkhand. It is part of the Mayurbhanj district and is home to tigers and elephants.

Answer:

Nanda Devi Biosphere Reserve is correctly matched with Uttarakhand.

Quick Tip:

India has 18 biosphere reserves, of which 12 are UNESCO-recognised. Nanda Devi is a common UPSC question because the Valley of Flowers (within the reserve) is frequently asked about in a separate context.

Understanding:

This question tests knowledge of the specific greenhouse gases (GHGs) covered under the Kyoto Protocol.

Step 1: Greenhouse gases listed under the Kyoto Protocol

The Kyoto Protocol specifically covers six greenhouse gases (later expanded by the Doha Amendment to seven with NF3 added):

1. Carbon dioxide (${\text{CO}}_2$)

2. Methane (${\text{CH}}_4$)

3. Nitrous oxide (${\text{N}}_2\text{O}$)

4. Hydrofluorocarbons (HFCs)

5. Perfluorocarbons (PFCs)

6. Sulphur hexafluoride (${\text{SF}}_6$)

Step 2: Role of nitrogen

Nitrogen (${\text{N}}_2$) constitutes approximately 78% of Earth's atmosphere but is NOT a greenhouse gas. It does not trap infrared radiation and is therefore not listed under the Kyoto Protocol or any other climate agreement as a GHG. Nitrogen gas is largely inert in the atmosphere.

Step 3: Distinguishing nitrous oxide from nitrogen

Nitrous oxide (${\text{N}}_2\text{O}$) is a powerful GHG (Global Warming Potential approximately 298 times that of ${\text{CO}}_2$ over 100 years) and IS listed. Nitrogen gas (${\text{N}}_2$) is entirely different.

Answer:

Nitrogen (${\text{N}}_2$) is NOT a greenhouse gas and is not covered by the Kyoto Protocol.

Quick Tip:

A common trap in exams is confusing nitrogen gas (${\text{N}}_2$) with nitrous oxide (${\text{N}}_2\text{O}$). Only ${\text{N}}_2\text{O}$ is a GHG. Sulphur hexafluoride has the highest GWP among Kyoto gases — worth remembering.

Understanding:

This question tests knowledge of the IUCN Red List categories, which are internationally recognised standards for assessing species extinction risk.

Step 1: IUCN Red List categories

The IUCN Red List uses a set of criteria to evaluate the extinction risk of species. The threat categories from highest (most endangered) to lowest are:

Step 2: Applying to the question

Among the options given, the correct descending order of threat is: Critically Endangered → Endangered → Vulnerable → Near Threatened.

Step 3: Why other options are wrong

Placing Endangered before Critically Endangered, or Vulnerable before Endangered, inverts the scale of threat severity.

Answer:

The correct order from most to least threatened is Critically Endangered → Endangered → Vulnerable → Near Threatened.

Quick Tip:

Remember: CE → E → V → NT → LC as a descending threat scale. The Great Indian Bustard is Critically Endangered; the tiger is Endangered on the global IUCN list (though recovering in India).

Understanding:

This question distinguishes between in-situ and ex-situ conservation strategies, a fundamental concept in biodiversity management.

Step 1: In-situ conservation defined

In-situ conservation means protecting species within their natural habitat or ecosystem. The term is derived from Latin, meaning 'on site.' It preserves not just individual species but also the ecological processes, interactions, and evolutionary potential of the species in their native environment.

Step 2: Examples of in-situ conservation

Protected areas such as national parks (e.g., Jim Corbett, Kaziranga), wildlife sanctuaries, biosphere reserves, sacred groves, and community conserved areas all constitute in-situ conservation. India's network of over 900 protected areas exemplifies this approach.

Step 3: Ex-situ conservation

Ex-situ conservation (Latin: 'off site') involves conserving species outside their natural habitat. This includes zoos, botanical gardens, gene banks, seed banks, cryogenic preservation, and captive breeding programmes. Options A, C, and D all describe ex-situ methods.

Answer:

In-situ conservation refers to the protection of species in their natural habitat through mechanisms such as national parks and wildlife sanctuaries.

Quick Tip:

In-situ = in nature; ex-situ = outside nature. The Convention on Biological Diversity (CBD) prioritises in-situ conservation as the primary approach, with ex-situ as a supplementary measure.

Understanding:

This question is about the structure of Earth's atmosphere and the location of the protective ozone layer.

Step 1: Layers of the atmosphere

Earth's atmosphere is divided into layers (from lowest to highest): Troposphere (0–12 km), Stratosphere (12–50 km), Mesosphere (50–80 km), Thermosphere (80–700 km), and Exosphere (above 700 km).

Step 2: Location of the ozone layer

The ozone layer is concentrated primarily in the stratosphere, between approximately 15 and 35 km above Earth's surface. Ozone (O3) in this layer absorbs most of the Sun's ultraviolet-B (UV-B) and UV-C radiation, protecting life on Earth from their harmful effects including skin cancer, cataracts, and damage to ecosystems.

Step 3: Tropospheric ozone

While ozone also exists in the troposphere, this ground-level ozone is a pollutant (a component of smog) rather than a protective layer. The stratospheric ozone is what is referred to as the 'ozone layer.'

Step 4: Montreal Protocol

The Montreal Protocol (1987) successfully regulated substances that deplete the ozone layer (ODS), such as chlorofluorocarbons (CFCs), leading to gradual recovery of the ozone layer.

Answer:

The ozone layer is found primarily in the stratosphere, at altitudes of approximately 15–35 km.

Quick Tip:

Good ozone is in the stratosphere (protects life); bad ozone is in the troposphere (pollutant and health hazard). The 'ozone hole' is observed over Antarctica and is monitored annually.

Understanding:

This question tests knowledge of India's Ramsar sites and specifically which site was first designated under the Ramsar Convention.

Step 1: India and the Ramsar Convention

India signed the Ramsar Convention in 1982. As of 2023, India has over 75 Ramsar sites, the highest number for any country in Asia.

Step 2: First Ramsar sites in India

Chilika Lake in Odisha and Keoladeo Ghana (Bharatpur Bird Sanctuary) in Rajasthan were both designated as India's first Ramsar sites in 1981, the year they were notified (though India formally joined Ramsar in 1982). Chilika Lake is generally listed first and is considered the first Ramsar site in India.

Step 3: Significance of Chilika Lake

Chilika Lake is the largest coastal lagoon in India and the second largest in the world. It is a critical habitat for migratory birds, the Irrawaddy dolphin, and numerous fish species. It was also the first site in Asia to be removed from the Montreux Record (a list of threatened Ramsar sites) following successful conservation efforts.

Answer:

Chilika Lake, Odisha, is recognised as the first Ramsar site designated in India.

Quick Tip:

Chilika Lake and Keoladeo Ghana were designated together in 1981. Chilika is listed first. Remember: Chilika is famous for the Irrawaddy dolphin and migratory flamingos — facts that appear independently in UPSC questions.

Understanding:

This question is about biomagnification, an ecological process with significant implications for environmental health and toxicology.

Step 1: Definition of biomagnification

Biomagnification (also called biological magnification or bioamplification) refers to the increasing concentration of a persistent toxic substance — such as DDT, mercury, or PCBs — as it moves up through the food chain from one trophic level to the next.

Step 2: Mechanism

Toxic, fat-soluble (lipophilic) and non-biodegradable substances are not metabolised or excreted efficiently. They accumulate in the fatty tissues of organisms (bioaccumulation). As larger organisms eat many smaller ones, they ingest and concentrate the toxin further. By the time the toxin reaches top predators (e.g., eagles, humans), its concentration may be thousands or millions of times higher than in the water or soil.

Step 3: Classic example

The classic example is DDT accumulation: DDT in water → phytoplankton → small fish → large fish → fish-eating birds (e.g., the bald eagle), where DDT caused eggshell thinning and reproductive failure. Mercury biomagnification in marine food chains (Minamata disease in Japan) is another landmark case.

Step 4: Distinguishing from bioaccumulation

Bioaccumulation refers to the build-up of a toxin in a single organism. Biomagnification is the increase in concentration across trophic levels.

Answer:

Biomagnification is the progressive increase in concentration of a toxic substance in organisms at successively higher trophic levels.

Quick Tip:

A useful mnemonic: 'Bigger eats more, gets more toxin.' Top predators and humans are most at risk from biomagnification. This is why mercury levels are highest in large fish like tuna and swordfish.

Understanding:

This question tests factual knowledge of the temperature targets enshrined in the Paris Agreement, the landmark international climate treaty adopted in December 2015.

Step 1: Paris Agreement temperature target

Article 2 of the Paris Agreement sets the long-term temperature goal: to hold the increase in global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognising that this would significantly reduce the risks and impacts of climate change.

Step 2: Significance of the 1.5°C target

The 1.5°C aspiration was included at the insistence of small island developing states and other vulnerable countries facing existential climate risks. The IPCC's 2018 Special Report on Global Warming of 1.5°C highlighted that even half a degree of additional warming causes significantly greater harm.

Step 3: Net zero target

The Paris Agreement calls for net zero emissions in the second half of the 21st century (not by 2030). Countries set their own net zero targets through NDCs (Nationally Determined Contributions). India's NDC pledges net zero by 2070.

Answer:

The Paris Agreement aims to limit global warming to well below 2°C, with efforts to limit it to 1.5°C above pre-industrial levels.

Quick Tip:

Remember the 2°C/1.5°C distinction carefully — UPSC questions sometimes present 3°C or 2.5°C as plausible distractors. The 1.5°C target was reinvigorated by the Glasgow Climate Pact (COP26, 2021).

Understanding:

We need to identify the correct working principle of a Scanning Electron Microscope (SEM), distinguishing it from related instruments.

Step 1: What SEM does

An SEM scans a focused beam of electrons across the surface of a specimen. When the electron beam interacts with atoms on the surface, it causes the emission of secondary electrons and backscattered electrons. Detectors collect these emissions, and the signal intensity at each point is used to construct a detailed three-dimensional-looking image of the surface morphology.

Step 2: Ruling out the other options

X-ray-based transmission imaging describes an X-ray diffractometer or X-ray imaging system, not an SEM. Visible light with optical lenses describes a conventional light (optical) microscope, limited to about 2000× magnification. A sharp metallic tip and quantum tunneling describes a Scanning Tunneling Microscope (STM), a different instrument capable of imaging individual atoms.

Step 3: Key distinction

SEM is specifically used for surface imaging and can achieve magnifications from about 20× to over 500,000×, with a resolution down to a few nanometres. It does not transmit electrons through the sample (that is the Transmission Electron Microscope, TEM).

Answer:

The SEM works by scanning an electron beam over the sample surface and detecting secondary and backscattered electrons to form a high-resolution surface image.

Quick Tip:

Remember the trio — SEM (surface imaging via secondary electrons), TEM (transmission through thin samples), STM (atomic-scale imaging via quantum tunneling). UPSC often tests these distinctions.