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UPSC Prelims 2019 · GS Paper I: In the context of proposals to the use of hydrogen-enriched CNG (H-CNG) as fuel…

Environment & Ecology
UPSC Prelims 2019 · GS Paper I

In the context of proposals to the use of hydrogen-enriched CNG (H-CNG) as fuel for buses in public transport, consider the following statements :

  • 1. The main advantage of the use of H-CNG is the elimination of carbon monoxide emissions.
  • 2. H-CNG as fuel reduces carbon dioxide and hydrocarbon emissions.
  • 3. Hydrogen up to one-fifth by volume can be blended with CNG as fuel for buses.
  • 4. H-CNG makes the fuel less expensive than CNG.

Which of the statements given above is/are correct?

Answer (b) & explanation

Statements 2 and 3 are correct (b). H-CNG blends hydrogen into compressed natural gas. Statement 3 is right because about 18–20% hydrogen by volume, roughly one-fifth, can be used in bus engines with small changes. Statement 2 is right because burning less carbon lowers CO₂ and hydrocarbon emissions. Statement 1 is wrong because it reduces carbon monoxide, by up to about 70%, but does not eliminate it. Statement 4 is wrong because hydrogen costs more than natural gas, so H-CNG is dearer than plain CNG.

Delhi ran trials on H-CNG buses from 2020. Notice the National Green Hydrogen Mission (2023), which aims at 5 million tonnes of green hydrogen a year by 2030, with hydrogen buses in Leh and Delhi.

Trap

"elimination" is too strong; H-CNG reduces CO, not removes it.

Answer as per the official UPSC answer key.

Learn the concept

ExplainerGreen Hydrogen: Colours of Hydrogen, Electrolysis, National Green Hydrogen Mission, Uses, Costs and Challenges (UPSC Notes + PYQs)

Same theme in UPSC Mains

Related questions from other years

UPSC Prelims 2026 · GS Paper I

Which of the following statements in relation to NIRANTAR (National Institute for Research and Application of Natural Resources to Transform, Adapt and Build Resilience), a platform of institutions under the Ministry of Environment, Forest and Climate Change, is/are correct ?

  • 1. Ecosystem Survey and Analysis is a vertical under this platform, the lead institute of which is Botanical Survey of India, Kolkata.
  • 2. Research and Management of Ecosystem Service is a vertical under this platform, the lead institute of which is Central Zoo Authority, New Delhi.
  • 3. Capacity Development Support is a vertical under this platform, the lead institute of which is Indian Institute of Forest Management, Bhopal.

Select the answer using the code given below :

Answer (b) & explanation

Statements 1 and 3 are correct (b). NIRANTAR groups the Environment Ministry's institutes into verticals. Statement 1 is right: Ecosystem Survey and Analysis is led by the Botanical Survey of India, Kolkata, with bodies like the FSI and ZSI. Statement 3 is right: Capacity Development Support is led by the Indian Institute of Forest Management, Bhopal. Statement 2 is wrong: Research and Management of Ecosystem Service is led by ICFRE, Dehradun; the Central Zoo Authority is only a member. So options (a), (c) and (d) fail.

Notice the purpose: pooling institutes avoids duplicate work and links research to climate adaptation and resilience. Other Ministry bodies include the Wildlife Institute of India (Dehradun) and GBPNIHE for the Himalaya.

Trap

the Central Zoo Authority does sit in that vertical, but as a member, not the lead.

Answer as per the official UPSC answer key.

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UPSC Prelims 2026 · GS Paper I

Consider the following statements with reference to India’s response to climate change :

  • I. India’s Long-Term Low Emission Development Strategy (LT-LEDS) is a crucial tool for achieving net-zero emissions by 2070.
  • II. India’s 4th Biennial Update Report (BUR-4) submitted in December, 2024 recorded around 8% decrease in Greenhouse gas emissions in 2020 over 2019.
  • III. Climate-resilient development necessarily depends on quick and short-term achievement of emission reduction targets.

Which of the following relationships among the above statements is/are correct ?

  • 1. Statement I is empirically supported by statement II.
  • 2. Statement III contradicts the approach implicit in statement I.
  • 3. Statement I and statement III together establish the premise of long-term sustainability.

Select the answer using the code given below :

Answer (b) & explanation

Relationships 1 and 2 are correct (b). Relationship 1 is right: the LT-LEDS (2022) lays out India's path to net zero by 2070, and BUR-4 reported a fall of about 7.9% in 2020 emissions over 2019, real data in line with that path. Relationship 2 is right: Statement III wants quick, short-term cuts, while the LT-LEDS is a long, gradual plan, so III contradicts I. Relationship 3 is wrong: two contradicting statements cannot together set a premise. So options (a), (c) and (d) fail.

Notice the cause of the 2020 fall: the COVID-19 lockdowns, not a lasting trend. India's updated NDC (2022) targets cutting emissions intensity of GDP by 45% from 2005 levels by 2030. Biennial Transparency Reports now replace BURs.

Trap

"together establish" sounds positive, but two statements that clash cannot form one premise.

Answer as per the official UPSC answer key.

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UPSC Prelims 2026 · GS Paper I

With respect to the Western Hoolock Gibbons, which of the following statements is/are correct ?

  • 1. A Sanctuary in North-east India is home to this ape species listed as Endangered in the International Union for Conservation of Nature (IUCN) Red List.
  • 2. They have specialized brachiation and can easily swing between trees.
  • 3. They possess a strong and heavy build like gorillas, yet are remarkably agile tree climbers.

Select the answer using the code given below :

Answer (b) & explanation

Statements 1 and 2 are correct (b). Statement 1 is right: India's only ape, the western hoolock gibbon, is Endangered on the IUCN Red List and gives its name to the Hollongapar Gibbon Sanctuary in Assam. Statement 2 is right: gibbons move by brachiation, swinging arm over arm through the canopy. Statement 3 is wrong: they are "lesser apes", slim and light, about 6–9 kg, nothing like a heavy gorilla. So options (a), (c) and (d) fail.

Notice their habits: they live in pairs with their young and sing loud duets at dawn. They are found south of the Brahmaputra in the North-East. Rail lines cutting through Hollongapar have raised concern, and canopy bridges were proposed to help them cross.

Answer as per the official UPSC answer key.

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UPSC Prelims 2026 · GS Paper I

Which of the following best explain(s) the rationale for protecting mangrove ecosystems in the context of climate resilience ?

  • 1. Mangroves reduce tidal energy and store freshwater, making them ideal sites for paddy cultivation in saline estuarine belts.
  • 2. Their salt-sensitive roots filter seawater, making mangroves key to converting coastal land into freshwater aquaculture zones.
  • 3. By withstanding tidal surges and offering biomass resources, mangroves function both as natural bio-shields and livelihood bases for rural communities.

Select the answer using the code given below :

Answer (d) & explanation

Only statement 3 explains the rationale (d). Statement 3 is right: by withstanding tidal surges and cyclones, mangroves act as natural bio-shields, and they offer biomass, such as fish, crabs, honey and fuel, for coastal villages. Statement 1 is wrong: mangroves do not store fresh water for paddy. Statement 2 is wrong: they are salt-tolerant, not salt-sensitive. Clearing them for farms or aquaculture ponds is exactly what harms them. So options (a), (b) and (c) fail.

Notice the proof: mangroves cut deaths in the 1999 Odisha super-cyclone and the 2004 tsunami. They also store much blue carbon. India's largest mangrove forest is the Sundarbans; the MISHTI scheme (2023) aims to plant more along the coast.

Trap

statement 2 says "salt-sensitive". Mangroves live in salt water because they tolerate it.

Answer as per the official UPSC answer key.

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