Which jet stream develops over the Indian peninsula during the season of the south-west monsoon?

The correct answer is B, the stratosphere. Ozone is concentrated in the lower and middle stratosphere, and because it absorbs ultraviolet radiation the temperature of this layer rises with height instead of falling. The same absorption shields life at the surface from harmful radiation, and the stability of the layer makes it free of cloud and turbulence, so aircraft fly in its lower part.

Option A, the troposphere, is the layer of weather, where temperature falls with height and where all cloud and rain occur. Option C, the mesosphere, lies above the stratosphere; it holds very little gas, has the lowest temperatures in the atmosphere and is where meteors burn up. Option D, the thermosphere, is much higher still and is known for its ionised layers that reflect radio waves, not for ozone.

The correct answer is A, about 6.5 degrees Celsius per kilometre. This is the average rate at which air temperature falls as one rises through the troposphere, and it explains why hill stations are cooler than the plains and why high peaks carry snow even in the tropics.

Option B is far too small and would leave the top of the troposphere warmer than it is. Option C is close to the dry adiabatic rate at which a parcel of rising air cools by expansion, which is a different idea from the lapse rate of the still atmosphere and is the commonest trap here. Option D is the same figure as the correct one with the decimal point moved, a deliberate distractor; note also that the lapse rate is an average, and on a cold clear night an inversion can make temperature rise with height near the ground.

The correct answer is B, the mesosphere. Although the air there is thin, it is dense enough to heat a body moving at cosmic speed by friction, so most meteors glow and are destroyed in this layer and are seen from the ground as shooting stars. The mesosphere also contains the coldest point of the atmosphere, the mesopause, at its top.

Option A, the stratosphere, lies below the mesosphere; by the time a meteor reaches that height it has usually burnt out. Option C, the thermosphere, lies above it and is so thin that although individual molecules are very energetic, there is not enough air to destroy an incoming body. Option D, the exosphere, is the outermost fringe where the atmosphere merges into space and where satellites orbit with almost no resistance.

The correct answer is B, nitrogen, which makes up about 78 per cent of dry air by volume. It is comparatively inert, so it dilutes oxygen and slows combustion, and it enters living things mainly through the nitrogen cycle in which bacteria fix it in a usable form.

Option A, oxygen, is second with about 21 per cent; it is essential for respiration and combustion, but a candidate who answers from importance rather than from quantity gets the question wrong. Option C, argon, is the most abundant of the inert gases in air at a little under one per cent. Option D, carbon dioxide, is only about four hundredths of one per cent, yet it matters out of all proportion to its quantity because it absorbs outgoing heat and drives the greenhouse effect, and its share is rising.

The correct answer is A, the eastern slopes of the Rockies. The wind is the Chinook. It descends the leeward slope, is compressed and warmed as it sinks, and can raise the temperature sharply in a few hours; it melts or evaporates the snow cover, which is why herders call it the snow eater and why it is valued for exposing the grass for cattle.

Option B is the home of the Foehn, a wind of exactly the same type and origin, but the name asked for here is the Chinook, and mixing the two is the standard trap. Option C is where the Zonda blows down from the Andes. Option D is the source region of the Sirocco, a hot and dusty wind that crosses the Mediterranean from the Sahara, which is not a descending mountain wind of this kind.