Which one of the following islands is the largest?

The correct answer is B, Desert, Tropical thorny, Moist deciduous, Mangrove. The route runs from the dry west to the wet east coast, so the vegetation changes as rainfall rises.

Bikaner lies in the Thar Desert of western Rajasthan, where rainfall is below about 25 cm and only desert plants such as khejri and cactus grow. Moving east through eastern Rajasthan and the drier parts of central India, rainfall of roughly 25 to 70 cm supports tropical thorn forests of acacia, babool and ber. Further east, in Chhattisgarh, Jharkhand and Odisha, rainfall of about 100 to 200 cm supports moist deciduous forests of sal and teak. Konark is on the Odisha coast near the Mahanadi delta, where tidal creeks support mangroves.

A is wrong: it puts thorny vegetation before the desert, but Bikaner itself is in the desert.

C is wrong: it starts with moist deciduous forest and ends with desert, the reverse of the journey.

D is wrong: mangroves grow only at the coast, so they must come last, after the inland deciduous forests.

Exam tip: more rain, richer forest: desert < thorn < dry deciduous < moist deciduous < evergreen; mangroves on tidal coasts.

The correct answer is D, Olivine. Olivine is a silicate of magnesium and iron that forms greenish crystals and is common in basalt.

Olivine takes its name from its olive-green colour. It crystallises early from hot magma that is low in silica, which is why it turns up in basalt, gabbro and peridotite and makes up much of the Earth's upper mantle. Its main elements are magnesium, iron and silica. A clear, gem-quality olivine is sold as the jewel peridot. Feldspar and quartz, by contrast, are the commonest minerals of the crust and are richer in silica.

A is wrong: amphibolite is a metamorphic rock made mostly of amphibole minerals, not a single mineral.

B is wrong: feldspar is made of silicon and oxygen with sodium, potassium, calcium and aluminium, and is light cream to salmon pink.

C is wrong: pyroxene contains calcium and aluminium along with magnesium, iron and silica, and is usually green or black.

Exam tip: olivine = green, Mg-Fe silicate, basalt, gem peridot; feldspar = half of the crust.

The correct answer is C, Both 1 and 2. S-waves are transverse waves: they shake the ground at right angles to their direction of travel, and that sideways motion forms crests and troughs.

An earthquake sends out two kinds of body waves. P-waves (primary) are the fastest and work like sound waves, pushing and pulling the material in the same direction as the wave moves; they pass through solids, liquids and gases. S-waves (secondary) arrive later and vibrate the material perpendicular to the wave direction in the vertical plane, which is why they create troughs and crests. S-waves travel only through solids, and their absence beyond the shadow zone told scientists that the outer core is liquid.

A is wrong: statement 2 is also correct, since the perpendicular vibration is what defines an S-wave.

B is wrong: statement 1 is correct too, as the crests and troughs follow from that vibration.

D is wrong: both statements describe S-waves accurately.

Exam tip: P-waves are longitudinal and go through all states of matter; S-waves are transverse and go through solids only.

The correct answer is C, Statement I is true but Statement II is false. Plantations do lie mostly in the humid tropics, but the soils there are generally poor, not highly fertile.

Plantation farming grows a single cash crop such as tea, coffee, rubber, sugarcane, cocoa, banana or oil palm on large estates with heavy capital and hired labour. It spread in the humid tropics of Asia, Africa and Latin America, largely under colonial rule, because these crops need high temperatures and heavy rain throughout the year. The same heavy rain leaches nutrients out of the soil, leaving laterite and other weathered red soils that are low in humus and plant food; the lush forest survives by quickly recycling nutrients from fallen leaves.

A is wrong: Statement II is false, so it cannot explain Statement I.

B is wrong: it treats the false Statement II as true.

D is wrong: Statement I is true and Statement II is false, the reverse of this option.

Exam tip: humid tropics have lush forest but leached, infertile laterite soil; plantations need the climate, not rich soil.

The correct answer is A, 1 only. In January the northern oceans are warmer than the frozen continents, so isotherms bend north over the sea and south over the land; the Gulf Stream and North Atlantic Drift are warm currents, not cold ones.

Isotherms are lines joining places of equal temperature. In the northern hemisphere winter, land loses heat quickly and becomes very cold, while the ocean keeps its warmth. A given temperature is therefore found further north over the ocean and further south over the continents such as Siberia, which makes the lines bend. Statement 2 is wrong: the Gulf Stream and the North Atlantic Drift carry warm tropical water into the North Atlantic, making it warmer, and that warmth is why the isotherms bend sharply north there, keeping ports of north-west Europe ice-free.

B is wrong because statement 2 calls warm currents cold.

C is wrong because statement 2 is false.

D is wrong because statement 1 is a correct inference.

Exam tip: January isotherms bend poleward over oceans and equatorward over land; Gulf Stream and North Atlantic Drift are warm currents.