Earth, landforms & geomorphology

Answer: (d) Rann of Kutch

The Rann of Kachchh was once a shallow part of the Arabian Sea. A geological shift closed off its connection with the sea, leaving a vast seasonal marshy salt desert that fills with water in the monsoon and dries into a white salt flat in summer.

• ✓ (d) The Rann was a shallow part of the Arabian Sea until a geological shift closed its connection with the sea; it is now a huge seasonal marshy salt desert in Gujarat, made up of the Great Rann and the Little Rann.
• ✗ (a) Bhitarkanika in Odisha is a mangrove forest. NCERT notes that mangroves grow along coasts in salt marshes, tidal creeks, mud flats and estuaries, so it is a coastal tidal wetland, not marshland left behind by a retreating sea.
• ✗ (b) Marakkanam in Tamil Nadu is known for its coastal salt pans, where salt is made from seawater; these are small human-made works, not a vast natural marshland.

Remember · Rann of Kutch: former shallow part of the Arabian Sea, cut off by a geological shift; now a seasonal marshy salt desert (Great Rann and Little Rann) in Gujarat.

📘 Read it in NCERT: Class 11 India: Physical Environment, Ch 5 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink · Report an error

Answer: (a) Only one

Only pair 3 is correctly matched. Pairs 1 and 2 have their descriptions swapped: Cepheids are stars whose brightness varies in a regular cycle, and nebulae are giant clouds of gas and dust. Pulsars are indeed neutron stars left when a massive star runs out of fuel and collapses.

• ✗ 1. Cepheids are pulsating variable stars, not clouds. Their regular changes in brightness are used to measure distances to galaxies.
• ✗ 2. A nebula is a very large cloud of gas (and dust), the place where stars form. It is not a star that brightens and dims.
• ✓ 3. A neutron star forms when a massive star runs out of fuel and its core collapses. Pulsars are neutron stars that spin fast and sweep a beam of radiation across space.

Remember · Cepheids are stars that brighten and dim in a regular cycle; nebulae are clouds of gas and dust; pulsars are spinning neutron stars.

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 2 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) Statement-I is incorrect but Statement-II is correct

The soil of a tropical rain forest is poor, not rich, in nutrients. Heat and moisture make bacterial action intense, so dead plant matter is oxidised quickly and very little humus builds up in the soil; heavy rain also leaches nutrients out of tropical soils.

• ✗ Statement-I Fast decay leaves the soil with very low humus content, and heavy rain leaches away nutrients; lateritic soils of heavy-rain tropical areas are generally deficient in plant nutrients.
• ✓ Statement-II In humid tropical and equatorial climates bacterial growth and action is intense, so dead vegetation is rapidly oxidised. This is the reason the humus content of the soil stays low, not a sign of richness.

Remember · Fast decay plus heavy rain leave tropical rain forest soil low in humus and nutrients; in cold climates decay is slow, so humus and peat accumulate.

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 5 (practise this chapter) · Class 10 Contemporary India – II, Ch 1 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (c) Both 1 and 2

Both statements are correct. P-waves travel faster, so a seismograph records them first, and they vibrate along the direction of travel. S-waves arrive later and vibrate at right angles to that direction.

• ✓ 1. P-waves are the primary waves: they move faster and are the first to reach the surface. S-waves, the secondary waves, arrive after a time lag, so they are recorded later.
• ✓ 2. P-waves vibrate parallel to the direction of the wave, pushing and squeezing the material to and fro. S-waves vibrate perpendicular to the wave direction in the vertical plane, so they create troughs and crests.

Remember · P-waves: primary, fastest, particles move to and fro along the path, pass through solids, liquids and gases. S-waves: secondary, slower, particles move up and down, only through solids.

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

Question and answer: UPSC's official GS Paper I (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error