Earth, landforms & geomorphology

Answer: (d) All four

An eruption brings out solid, liquid and gaseous material: lava, fragments of rock, fine ash and dust, and gases. The gases include nitrogen and sulphur compounds, so all four listed items are volcanic products.

• ✓ 1. Pyroclastic debris — rock fragments blown out by the explosion — is thrown out along with lava flows and volcanic bombs.
• ✓ 2. Fine ash and dust are ejected in eruptions and can spread over large areas.
• ✓ 3. Nitrogen compounds are among the gases released by volcanoes.
• ✓ 4. Sulphur compounds are also released as volcanic gases, alongside small amounts of chlorine, hydrogen and argon.

Remember · Volcanic output: lava, pyroclastic debris, volcanic bombs, ash and dust, and gases (nitrogen and sulphur compounds, minor chlorine, hydrogen, argon).

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 3 (practise this chapter)

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Answer: (a) Both Statement-II and Statement-III are correct and both of them explain Statement-I

Chemical weathering works through water, oxygen and carbon dioxide. Falling rain dissolves both gases from the air: the dissolved carbon dioxide forms a weak acid that attacks rocks (carbonation), and the dissolved oxygen oxidises minerals such as iron. So both II and III are true and each explains why rain weathers rock.

• ✓ Statement-I Rainwater drives chemical weathering processes such as solution, carbonation, hydration and oxidation.
• ✓ Statement-II Rain dissolves atmospheric carbon dioxide and becomes weakly acidic; this acid dissolves minerals, especially in limestone (carbonation). It explains Statement-I.
• ✓ Statement-III Rain also carries dissolved oxygen, which oxidises iron-bearing minerals and weakens the rock. It too explains Statement-I.

Remember · Chemical weathering needs water plus air — oxygen (oxidation) and carbon dioxide (carbonation). Rainwater brings both.

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 5 (practise this chapter) · Class 11 Fundamentals of Physical Geography, Ch 5 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) Only two

Rows 3 and 4 are right: the Appalachians and the Andes are fold mountains raised where plates converged. Row 1 is wrong twice over — the Vosges are in Europe (France) and are a block mountain beside the Rhine rift valley; row 2 is wrong because the Alps are young fold mountains, not block mountains.

• ✗ 1. The Vosges are in north-eastern France, west of the Rhine Graben — a sunken block of crust. They are a classic block (horst) mountain of Europe, not a fold range of Central Asia.
• ✗ 2. The Alps belong to the young zone of continental collision that runs from the Himalayas to Europe; they are fold mountains, not block mountains.
• ✓ 3. The Appalachians formed in continental collisions 500–300 million years ago; their sedimentary layers were folded and faulted. They are old, worn-down fold mountains.
• ✓ 4. The Andes were raised as the oceanic Nazca Plate pushed under the South American Plate — a convergent-boundary fold range.

Remember · Fold: Himalayas, Alps, Andes, Rockies (young); Appalachians, Aravallis, Urals (old). Block: Vosges and Black Forest on either side of the Rhine rift valley.

Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) 2 and 4

21 June is the summer solstice of the northern hemisphere, when the North Pole is tilted towards the Sun. Every place north of the equator then gets more than 12 hours of daylight, the equator gets exactly 12, and the southern hemisphere gets less. So the Tropic of Cancer and the Arctic Circle qualify.

• ✗ 1. The equator has about 12 hours of daylight and 12 hours of darkness throughout the year, never more.
• ✓ 2. The Tropic of Cancer is in the northern hemisphere, where days are longer than 12 hours in June; on 21 June the Sun is overhead there at noon.
• ✗ 3. The Tropic of Capricorn is in the southern hemisphere, where June is winter and daylight is shorter than 12 hours.
• ✓ 4. On 21 June the Arctic Circle has its longest day — the Sun stays above the horizon for about 24 hours.

Remember · 21 June: longest day north of the equator (24-hour day at and beyond the Arctic Circle); equator always ~12 hours; southern hemisphere has short winter days.

📘 Read it in NCERT: Class 7 Curiosity, Ch 12 (practise this chapter) · Class 7 Curiosity, Ch 12 (practise this chapter) · Class 7 Curiosity, Ch 12 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error