Karst topography takes its name from a plateau in which present-day country?

The correct answer is B, soil erosion. Bad lands are stretches of land cut into a close network of deep gullies and sharp ridges, so dissected that cultivation becomes impossible, and they are produced when running water removes the topsoil through sheet wash that concentrates first into rills and then into gullies. The Chambal ravines of Madhya Pradesh, Rajasthan and Uttar Pradesh are the Indian textbook example. Option A, scanty rainfall, is wrong because bad lands need intense, concentrated runoff on loose material, and they occur in areas of heavy seasonal downpours rather than in the driest tracts. Option C, excessive forest cover, is the opposite of the truth: a thick cover of roots and leaf litter binds soil and breaks the force of raindrops, so forests prevent gullying. Option D, open defecation, is a sanitation problem with no role in shaping gullies. Note that the same question is sometimes asked with the word ravine instead of bad land; the answer stays the same.

The correct answer is D, overgrazing. Overgrazing strips the protective cover of grass, loosens the surface with hooves and leaves bare soil exposed to rain and wind, so it is one of the leading causes of soil erosion in dry India, never a remedy. Option A, intercropping, grows two or more crops together in alternate rows so that the ground is never left bare, which cuts the force of falling rain and is a recognised conservation practice. Option B, shelter belts, are rows of trees planted across the prevailing wind, used in Rajasthan and in the coastal tracts to slow the wind and stop deflation of sandy soil. Option C, a rock dam, is a low barrier of rocks built across a gully so that water slows, drops its silt and stops cutting the channel deeper. Questions of this kind usually list three genuine measures and one cause of degradation, so read the stem for the word NOT.

The correct answer is B, II, IV, III and I. Water erosion passes through stages, and the soil lost grows at every stage. Splash erosion, numbered II, is the first and mildest: raindrops strike bare soil and knock single particles a few centimetres away. Sheet erosion, numbered IV, follows when the dislodged material is carried off as a thin film of water over the whole surface. Rill erosion, numbered III, begins when that flow gathers into small channels a few centimetres deep that a plough can still erase. Gully erosion, numbered I, is the final and most destructive stage, in which the rills deepen into permanent ravines and the field goes out of use. So the increasing order is splash, sheet, rill and gully, which is option B. Option A and option C both place gully or rill ahead of splash, and option D wrongly puts rill before sheet, so none of them matches the recognised sequence.

The correct answer is B, physical weathering. Exfoliation is caused by repeated heating and cooling of the outer layer of a rock and by the release of pressure when overlying material is removed; the surface expands and contracts more than the interior and splits away as curved sheets. No change in the chemical composition of the rock takes place, and nothing is transported, so the process is mechanical weathering in place. Option A, chemical weathering, would require reactions such as carbonation, hydrolysis or oxidation that alter the minerals themselves, as in the solution of limestone. Option C, glacial erosion, involves moving ice that plucks and abrades rock, producing cirques and U-shaped valleys, not onion-skin shells. Option D, wind deposition, builds dunes and loess sheets and is a depositional process, the opposite of breaking rock down. Remember the rule that decides most questions in this chapter: weathering breaks rock where it stands, erosion carries the pieces away.

The correct answer is C, groundwater. Rainwater charged with carbon dioxide becomes a weak carbonic acid, seeps along joints in limestone and dissolves calcium carbonate by carbonation. Inside a cavern the dripping water loses carbon dioxide and redeposits that calcium carbonate, building stalactites downward from the roof, stalagmites upward from the floor, and a pillar where the two meet. The whole family of such features belongs to karst topography. Option A, wind, produces mushroom rocks, yardangs, dunes and loess, all in dry regions with bare surfaces. Option B, glacier, carves cirques, aretes, horns and U-shaped valleys and deposits moraines and drumlins. Option D, sea waves, cut cliffs, caves, arches and stacks along a coast and build beaches, spits and lagoons. A useful memory hook is that a stalactite holds tight to the ceiling while a stalagmite might grow up from the ground.