Environment

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1.Which of the following best explains why the carbon isotope ratio (¹³C/¹²C) in marine carbonates can be used to infer past changes in the global carbon cycle?
  • AMarine carbonates directly record atmospheric CO₂ concentration
  • BThe ratio changes only with volcanic eruptions
  • CVariations in the ratio reflect shifts between organic carbon burial and carbonate precipitation
  • DIsotopic fractionation is constant across all geological periods

Explanation

Changes in the ¹³C/¹²C ratio in carbonates mirror the balance between burial of ¹³C‑depleted organic matter and precipitation of ¹³C‑enriched carbonates, providing a proxy for carbon cycle dynamics.
2.Which of the following mechanisms is NOT a positive feedback loop in the climate system?
  • AMelting of Arctic sea ice reducing albedo
  • BIncreased water‑vapor content enhancing greenhouse effect
  • CPlant growth accelerating CO2 uptake (CO2 fertilisation)
  • DPermafrost thaw releasing methane

Explanation

CO2 fertilisation can increase plant growth, thereby sequestering more carbon – a negative feedback. The other three processes amplify warming, constituting positive feedbacks.
3.The 'Delhi Air Quality Index' (AQI) categorises a value of 251–300 as:
  • AModerate
  • BUnhealthy for Sensitive Groups
  • CVery Unhealthy
  • DHazardous

Explanation

According to the CPCB AQI classification, 251–300 falls under the 'Very Unhealthy' category, indicating serious health impacts for the general population.
4.Which of the following research initiatives is most commonly associated with Biosphere Reserves under the MAB Programme?
  • ASpace exploration missions
  • BLong‑term ecological monitoring and socio‑ecological studies to assess human‑environment interactions
  • CDevelopment of nuclear weapons
  • DConstruction of high‑rise commercial complexes

Explanation

MAB encourages long‑term ecological research, monitoring of biodiversity, and studies on how human societies interact with ecosystems, providing data for sustainable management.
5.What proportion of the total carbon stored on Earth is found in the lithosphere (rocks and sediments)?
  • A~0.02%
  • B~0.2%
  • C~2%
  • D~66%

Explanation

About two‑thirds (≈66%) of Earth's carbon resides in the lithosphere as carbonate rocks and fossil fuels, making it the largest carbon reservoir.
6.

Q3. Which of the following is/are examples of Keystone Species?

  1. Tiger

  2. Sea Otter

  3. Elephant

  4. Honey Bee

Select the correct answer

  • A

    1 only

  • B

    1 and 2 only

  • C

    1, 2 and 3 only

  • D

    1, 2, 3 and 4

Explanation

Answer

✅ D. 1, 2, 3 and 4

Explanation

A Keystone Species has an ecological impact much greater than its population size.

Tiger

  • Controls herbivore population.

Sea Otter

  • Controls sea urchins.

  • Protects kelp forests.

Elephant

  • Creates grasslands.

  • Disperses seeds.

  • Creates water holes.

Honey Bee

  • Pollination.

  • Supports food production.

Loss of these species destabilizes ecosystems.

UPSC Angle

Differentiate:

  • Keystone species

  • Umbrella species

  • Flagship species

  • Indicator species

  • Endemic species

7.

Consider the following statements regarding HFC-23 destruction:

1.China recently reported destroying 17,000 metric tons of HFC-23 annually, equivalent to reducing over 250 million tons of CO₂ emissions.

2.HFC-23 is a potent greenhouse gas whose phase-down is a key component of the Kigali Amendment to the Montreal Protocol.

Which of the statements given above is/are correct?

  • A

    1 only

  • B

    2 only

  • C

    Both 1 and 2

  • D

    Neither 1 nor 2

Explanation

Both statements are correct. China’s reported destruction of HFC-23 has a massive CO₂-equivalent impact, and HFC-23 is a potent greenhouse gas targeted under the Kigali Amendment.

8.The term "biogenic carbon" refers to:
  • ACarbon derived from living or once‑living organisms
  • BCarbon formed in the mantle
  • CCarbon in the form of carbonates
  • DCarbon emitted from fossil‑fuel combustion

Explanation

Biogenic carbon originates from biological processes – it is carbon that is part of living organisms or has been part of them in the recent past.
9.

Global investment in clean energy reached a record $2.2 trillion in 2025. What was the primary motivation for 70 percent of this increase?

  • A

    A desire to lower corporate tax rates in advanced economies.

  • B

    Net importers of fossil fuels seeking to bolster national energy security.

  • C

    Global adherence to a 2026 UN ban on all internal combustion engines.

  • D

    Direct cash transfers from the World Bank to private solar firms.

Explanation

Energy security has become the main driver, as fossil fuel prices remained volatile. So What? The green transition is being "securitized." This means climate action is now driven by survival and sovereignty rather than just environmental altruism.

  • Why others are wrong: (A), (C), and (D) are not identified as the primary drivers in the report.

10.Which of the following gases is NOT a direct precursor for tropospheric ozone formation?
  • ANitrogen oxides (NOx)
  • BVolatile organic compounds (VOCs)
  • CSulphur dioxide (SO₂)
  • DCarbon monoxide (CO)

Explanation

Tropospheric ozone is produced through photochemical reactions involving NOx and VOCs (and CO can also participate). SO₂ is a precursor for sulfate aerosols, not ozone.

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