Consider the following statements : Statement-I : Thickness of the troposphere at the equator is much greater as compared to poles. Statement-II : At the equator, heat is transported to great heights by strong convectional currents. Which one of the following is correct in respect of the above statements?

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.

The correct answer is B, Only two. Mahua and teak shed their leaves in the dry season, while the jackfruit tree is evergreen.

Deciduous trees drop all their leaves for a few weeks in the dry summer to save water; they make up India's tropical moist and dry deciduous forests, the most widespread forest type in the country. Teak is the best-known tree of these forests, found in Madhya Pradesh, Maharashtra, Karnataka and Kerala. Mahua is a deciduous tree of central India whose flowers are eaten and used to make liquor, and whose seeds give oil; it matters greatly to tribal communities. The jackfruit, by contrast, keeps its glossy leaves all year and grows in the humid Western Ghats and coastal regions.

A is wrong because two of the trees, not one, are deciduous.

C is wrong because the jackfruit is evergreen.

D is wrong because teak and mahua are typical deciduous trees.

Exam tip: teak, sal, mahua, sandalwood = deciduous; jackfruit, rosewood, mahogany = evergreen.

The correct answer is D, All four. A volcanic eruption throws out solid fragments, fine ash and dust, and a mixture of gases that includes nitrogen and sulphur compounds.

Material released by a volcano is of three kinds. Solid matter includes pyroclastic debris, the broken pieces of rock and lava blown out by the explosion, ranging from large volcanic bombs to small lapilli, along with fine ash and dust that can spread across continents. Liquid matter is the lava. Gases are mostly water vapour, followed by carbon dioxide, sulphur compounds such as sulphur dioxide and hydrogen sulphide, and nitrogen compounds, with smaller amounts of chlorine, hydrogen and argon. Sulphur dioxide forms sulphate aerosols in the stratosphere that can cool the climate for a year or two.

A is wrong because more than one item is a volcanic product.

B is wrong because the gases, not only the solids, come from eruptions.

C is wrong because none of the four can be left out.

Exam tip: volcanic gases = mostly water vapour, then carbon dioxide, sulphur and nitrogen compounds.

The correct answer is B, Only two pairs. Pairs 1 and 2 are correct; Visakhapatnam is not India's largest container port.

Kamarajar Port at Ennore, near Chennai in Tamil Nadu, was the first major port in India to be set up as a corporate entity, registered as a public company (Ennore Port Ltd). Mundra Port in Kutch, Gujarat, run by the Adani group, is the largest privately owned port in India. Visakhapatnam in Andhra Pradesh is a major port known for iron ore and bulk cargo and has a deep natural harbour, but the biggest container traffic is handled on the west coast, at Jawaharlal Nehru Port (Nhava Sheva) and Mundra.

A is wrong because two pairs, not one, are correct.

C is wrong because pair 3 is incorrect.

D is wrong because pairs 1 and 2 are correctly matched.

Exam tip: Kamarajar (Ennore) = first corporatised major port; Mundra = largest private port; container giants are on the west coast.

The correct answer is D, Statement-I is incorrect, but Statement-II is correct. The atmosphere is heated mainly from below, by the Earth's own long wave (terrestrial) radiation, not directly by sunlight.

Incoming solar radiation is short wave, and the atmosphere is largely transparent to it, so most of it passes through and heats the Earth's surface. The warmed surface then gives off heat as long wave infrared radiation. Water vapour, carbon dioxide and other greenhouse gases absorb this long wave radiation well, and this is what warms the lower atmosphere. That is also why temperature normally falls with height in the troposphere.

A and B are wrong because Statement-I itself is false, so neither can be the answer.

C is wrong because it reverses the truth: Statement-I is the incorrect one, while Statement-II correctly describes greenhouse gases.

Exam tip: Sun gives short wave radiation that heats the ground; the ground gives long wave radiation that heats the air.