Earth, landforms & geomorphology

Answer: (c) Only four

The Andes run along South America's western side through seven countries: Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile and Argentina. From the list, Bolivia, Colombia, Ecuador and Venezuela lie on the chain; Brazil and Paraguay lie wholly to the east.

• ✓ I Bolivia is one of the countries with large portions of the Tropical Andes.
• ✗ II Brazil is not one of the Andean countries; it lies east of the chain, in the Amazon basin and the Brazilian Highlands.
• ✓ III Colombia includes large portions of the Tropical Andes; the northern Andes split into several ranges (cordilleras) there.
• ✓ IV Ecuador includes large portions of the Tropical Andes; its Andean cordilleras carry volcanoes such as Chimborazo and Cotopaxi.
• ✗ V Paraguay is a landlocked lowland country of the Paraná–Paraguay basin and the Gran Chaco, with no Andean ranges.
• ✓ VI The Andes hotspot extends from western Venezuela, where the northernmost Andes (the Venezuelan or Caribbean cordillera) lie.

Remember · Andes countries (7), north to south: Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile, Argentina. Not Brazil, Paraguay, Uruguay or the Guianas.

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Answer: (c) I, II and III

All three are classic evidences Wegener's supporters used to show the southern continents were once joined: matching ancient rock belts on either side of the South Atlantic, placer gold in Ghana whose source veins lie in Brazil, and the same glacial Gondwana sediments in India and five other southern landmasses.

• ✓ I Rocks about 2,000 million years old on the Brazilian coast match those of western Africa, and the oldest marine deposits along both coasts are only Jurassic, so the ocean between them is young.
• ✓ II Ghana has rich placer gold but no source rock; the gold-bearing veins are in Brazil, so the deposits must have come from the Brazil plateau when the continents touched.
• ✓ III The Gondwana sediments of India, with thick glacial tillite at the base, are matched in Africa, the Falkland Islands, Madagascar, Antarctica and Australia.

Remember · Continental drift evidence: jig-saw fit, matching rocks across the Atlantic (Brazil–West Africa), Ghana's placer gold from Brazil, Gondwana tillite in six southern landmasses, fossils like Mesosaurus and Glossopteris.

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Answer: (c) Only one of the Statements II and III is correct and that explains Statement I

Porosity is how much empty space a rock holds; permeability is how easily water passes through it. Chalk is a soft limestone, and limestone is porous and gives up its pore water freely, which explains Statement I. Clay is actually highly porous (USGS puts it at about 50%), but its pores are so tiny that water barely moves, so Statement III ('not at all porous') is wrong.

• ✓ Statement I Chalk is a variety of limestone (Britannica), and USGS shows limestone yielding most of its pore water freely, while groundwater moves very slowly through relatively impermeable materials such as clay and shale.
• ✓ Statement II Chalk, as a limestone, is porous: USGS lists limestone at 20% porosity with 18% specific yield, so it takes up and releases water readily. That is why chalk is permeable, so II explains I.
• ✗ Statement III Clay is not free of pores: USGS lists its porosity at 50%, but only 2% of that drains freely because the pores are tiny. Britannica notes that permeability falls as the average pore size becomes smaller.

Remember · Porosity = pore space; permeability = ease of water flow. Chalk (limestone): porous and permeable. Clay: highly porous but nearly impermeable because its pores are minute.

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Answer: (b) Both Statement II and Statement III are correct but only one of them explains Statement I

Both Statement II and Statement III are true, but only Statement III explains Statement I. Melting polar ice moves mass from the poles towards the equatorial ocean, and such shifts of mass change Earth's rotation and axis. A solar storm heats the upper atmosphere but does not shift the planet's mass, so it cannot explain a change in rotation or axis.

• ✓ I NASA-funded studies show Earth's spin axis drifts (polar motion) and its rotation slows, as mass is redistributed on and within the planet.
• ✓ II Solar flares and coronal mass ejections do hit Earth's upper atmosphere with charged particles and energy and can heat it. This is a space-weather effect and does not move Earth's mass, so it does not explain Statement I.
• ✓ III Faster melting of ice sheets has shifted mass from the poles towards the equatorial ocean. This redistribution of mass is the cause of the change in rotation and axis, so it explains Statement I.

Remember · Ice melt shifts mass from the poles to the equatorial oceans, changing Earth's spin axis and lengthening the day; solar storms only affect the upper atmosphere.

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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).

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Answer: (c) Pennar

The Gandikota gorge in Kadapa district, Andhra Pradesh, is cut by the Pennar (Penna) river through the Erramala hills. The name itself joins the Telugu words for gorge ('gandi') and fort ('kota'), after the medieval fort perched above the canyon.

• ✓ (c) The Kadapa district administration describes the Penna river gorge, about 200 metres wide, flowing between the cliffs of the Erramala hills at Gandikota.
• ✗ (d) The Tungabhadra is a Krishna tributary flowing past Hampi in Karnataka; it does not flow through Kadapa district.
• ✗ (b) The Manjira is a tributary of the Godavari in Maharashtra, Karnataka and Telangana, far north of Gandikota.

Remember · Gandikota ('gorge fort'), Kadapa district, Andhra Pradesh: canyon of the Pennar/Penna river through the Erramala hills — often called India's Grand Canyon.

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Answer: (b) Second half of the month of June

The Northern Hemisphere's longest day is the summer solstice, around 21 June, when the North Pole is tilted most towards the Sun and the Sun is overhead at the Tropic of Cancer. 21 June falls in the second half of June.

• ✓ (b) The summer solstice falls on 20, 21 or 22 June; after it, days in the Northern Hemisphere grow shorter and nights longer.
• ✗ (a) Days are still lengthening through the first half of June; the maximum comes only at the solstice around 21 June.
• ✗ (c) July is often the hottest month because of the lag in heating, but day length is already decreasing by then.

Remember · Summer solstice ~21 June: Sun overhead at the Tropic of Cancer, longest day in the Northern Hemisphere; winter solstice ~22 December: shortest day.

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Answer: (b) 2 only

Only statement 2 is correct: ice caps and glaciers hold about 2 per cent of Earth's water, well above the 0.68 per cent held as groundwater, while rivers and lakes together hold only about 0.009 per cent.

• ✗ 1. NCERT's table gives fresh water lakes 0.009 per cent and rivers 0.0001 per cent of all water, far less than groundwater at 0.68 per cent.
• ✓ 2. The same table gives ice caps 2.0 per cent (glaciers are counted with them), which is roughly three times the groundwater share of 0.68 per cent.

Remember · Earth's water: oceans 97.3%, ice caps and glaciers 2.0%, groundwater 0.68%, lakes 0.009%, atmosphere 0.0019%, rivers 0.0001%.

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Answer: (b) fissure volcanic rock

Black cotton soil (regur) forms from the weathering of the basalt lava that poured out of fissures to make the Deccan Traps, so the parent rock is fissure volcanic rock.

• ✓ (b) NCERT calls black soil typical of the Deccan trap (basalt) region and says it is made up of lava flows. The Deccan Traps are a flood basalt province built by lava outpourings through cracks in the crust.
• ✗ (c) Granite and schist are crystalline rocks; NCERT links red soil, not black soil, with crystalline igneous rocks on the Deccan plateau.
• ✗ (a) Brown forest soil is itself a soil, not a rock, so it cannot be the rock whose weathering produces black soil.
• ✗ (d) Shale and limestone are sedimentary rocks; black soil forms from volcanic basalt.

Remember · Black (regur) soil comes from Deccan Trap basalt, which erupted from fissures; it holds moisture well and suits cotton.

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Answer: (a) does not set below the horizon at the Arctic Circle

21 June is the June (northern summer) solstice: the North Pole is tilted towards the Sun, the noon Sun is overhead at the Tropic of Cancer, and every place on or north of the Arctic Circle (about 66½° N) has the Sun above the horizon for the full 24 hours.

• ✓ (a) The Arctic Circle is defined as the southern limit of the zone where the Sun does not set on at least one day a year — the June solstice.
• ✗ (b) On the same day the Antarctic Circle has the opposite: the Sun does not rise, giving 24 hours of night.
• ✗ (c) The noon Sun is overhead at the Equator only at the equinoxes (around 21 March and 23 September).
• ✗ (d) The Sun is overhead at the Tropic of Capricorn at the December solstice (around 22 December); on 21 June it is over the Tropic of Cancer.

Remember · 21 June: Sun overhead at Tropic of Cancer; midnight sun at and north of the Arctic Circle; polar night at the Antarctic Circle. Reversed around 22 December.

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Answer: (c) 1 and 3 only

Statements 1 and 3 are correct. The Earth's magnetic field has flipped repeatedly in the geological past, and early life released oxygen that changed the atmosphere. Statement 2 is false because the early atmosphere had carbon dioxide and very little free oxygen.

• ✓ 1. Rocks record past polarity flips of the magnetic field. NASA describes a history of flipping every few hundred thousand years, though the flips are irregular and the last was about 780,000 years ago.
• ✗ 2. The early atmosphere was mostly water vapour, nitrogen, carbon dioxide, methane and ammonia, with very little free oxygen. It was not 54% oxygen and it did contain carbon dioxide.
• ✓ 3. Once life evolved in the oceans, photosynthesis added oxygen to the water and later the air. About 2,000 million years ago oxygen began to flood the atmosphere.

Remember · Early atmosphere: water vapour, nitrogen, CO2, methane, ammonia, almost no free oxygen. Oxygen came from photosynthesis by early life.

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Answer: (a) 1 only

Only statement 1 is correct: Barren Island, in the Andaman Sea, is India's only active volcano. It lies north-east of Port Blair, not east of Great Nicobar, and it has erupted again after 1991, most recently in 2017 as of the exam.

• ✓ 1. NCERT calls Barren Island, in the Andaman and Nicobar Islands, the only active volcano in India.
• ✗ 2. The island is about 138 km north-east of Port Blair (now Sri Vijaya Puram), the capital of the Andaman and Nicobar Islands. Great Nicobar is at the far southern end of the island chain, much farther away.
• ✗ 3. The volcano did not stay quiet after 1991; the Ministry of Tourism's page says it last erupted in 2017.

Remember · Barren Island, about 138 km north-east of Port Blair, is India's only active volcano and has erupted as recently as 2017.

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