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Exploration

Class 9 · Science & Environment

Ch 13 · Earth as a System: Energy, Matter, and Life

Real UPSC Prelims questions from 2016–2026, linked to this book. Try each one first, then open the answer. 2026 answers follow UPSC's provisional answer key.

Prelims 2018 · Q65

Which of the following statements best describes "carbon fertilization"?

(a)Increased plant growth due to increased concentration of carbon dioxide in the atmosphere
(b)Increased temperature of Earth due to increased concentration of carbon dioxide in the atmosphere
(c)Increased acidity of oceans as a result of increased concentration of carbon dioxide in the atmosphere
(d)Adaptation of all living beings on Earth to the climate change brought about by the increased concentration of carbon dioxide in the atmosphere

Show answer

UPSC's answer: (a)

NCERT answers it: Class 11 Fundamentals of Physical Geography, Ch 11 (World Climate and Climate Change); Class 9 Exploration, Ch 13 (Earth as a System: Energy, Matter, and Life).

How to solve it with NCERT: Class 11 Fundamentals of Physical Geography, ch 11: forests use CO2 in their growth. Warming (b) is the greenhouse effect, and more acidic sea water (c) is a separate effect, named in Class 9 Exploration, ch 13. 'Fertilization' means growth. Answer (a).

Hindi version: UPSC's official question paper (2018), question 65 ↗

Prelims 2021 · Q27

In case of which one of the following biogeochemical cycles, the weathering of rocks is the main source of release of nutrient to enter the cycle?

(a)Carbon cycle
(b)Nitrogen cycle
(c)Phosphorus cycle
(d)Sulphur cycle

Show answer

UPSC's answer: (c)

NCERT answers it: Class 12 Biology, Ch 12 (Ecosystem); Class 9 Exploration, Ch 13 (Earth as a System: Energy, Matter, and Life).

The one fact NCERT doesn't give: Phosphorus has no stable gaseous form in the air, unlike carbon, nitrogen and sulphur, so it enters the cycle mainly from rocks as they weather.

Class 12 Biology, ch 12: the carbon cycle's reservoir is the air or water, but the phosphorus cycle's reservoir is the Earth's crust. Class 9 Exploration, ch 13: nitrogen's largest reservoir is the air. Class 10 Contemporary India II, ch 6: sulphur dioxide is one of the gases in polluted air. With the fact, only phosphorus has to come from rocks. Answer (c).

Hindi version: UPSC's official question paper (2021), question 27 ↗

Prelims 2025 · Q29

Consider the following statements:

I.Without the atmosphere, temperature would be well below freezing point everywhere on the Earth's surface.
II.Heat absorbed and trapped by the atmosphere maintains our planet's average temperature.
III.Atmosphere's gases, like carbon dioxide, are particularly good at absorbing and trapping radiation.

Which of the statements given above are correct?

(a)I and III only
(b)I and II only
(c)I, II and III
(d)II and III only

Show answer

UPSC's answer: (c)

NCERT answers it: Class 9 Exploration, Ch 13 (Earth as a System: Energy, Matter, and Life).

How to solve it with NCERT: Class 9 Exploration (Science), ch 13: greenhouse gases such as CO2 absorb the heat the Earth gives off (III), which keeps the planet warm (II). Without the atmosphere the Earth would be too cold for life (I). All three. Answer (c).

Hindi version: UPSC's official question paper (2025), question 29 ↗

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