The winter rainfall of Punjab, Haryana and western Uttar Pradesh is caused by:

The correct answer is A, the north-east monsoon. As the monsoon retreats in October and November the wind direction reverses and air moves from the land towards the sea. Crossing the Bay of Bengal it picks up moisture and strikes the Coromandel coast, giving Tamil Nadu and coastal Andhra Pradesh their main rainy season. This is why Tamil Nadu is the one large part of India whose farming calendar depends on winter rather than summer rain.

Option B, local air circulation, produces land and sea breezes that are too small to give a season of rain. Option C, temperate cyclones, are the western disturbances, and they bring winter rain to the north-west of India, not to the far south. Option D, the south-west monsoon, leaves Tamil Nadu dry because the state lies in the rain shadow of the Western Ghats during those months.

The correct answer is D, Karnataka. The pre-monsoon thundery showers of Karnataka are called cherry blossom showers or blossom showers because they help the coffee plants of the Kodagu, Chikkamagaluru and Hassan belt to flower. The same family of pre-monsoon showers is called mango showers in Kerala and coastal Karnataka because it helps mangoes ripen, and the two names are often asked together.

Option A, Gujarat, has no such local shower in the standard list. Option B, Meghalaya, is known for the heaviest rainfall of the country at Mawsynram and Cherrapunji, but that rain comes from the Bay of Bengal branch of the monsoon. Option C, Uttarakhand, receives winter precipitation from western disturbances and monsoon rain in summer, and neither is called a blossom shower.

The correct answer is B, the monsoon trough. The monsoon trough is the belt of low pressure that lies across the northern plains during the rainy season and guides the depressions that bring rain. As the sun appears to move south of the equator after the September equinox, the land cools, the low pressure weakens and the trough is replaced by high pressure. That retreat of the trough is what is called the withdrawal or retreat of the monsoon, and it begins from north-west India in early September.

Option A, an upper level trough, belongs to the upper air circulation and is not the feature described here. Option C, a lee trough, forms on the sheltered side of a mountain and is a local feature. Option D, an inverted trough, is a name used for a monsoon trough that extends into the Bay of Bengal in a particular shape, not the plains feature that weakens in October.

The correct answer is B, isohyet. An isohyet is a line drawn on a map through all the places that receive the same amount of rainfall in a given period. Rainfall maps of India are drawn with isohyets, and the crowding of these lines along the Western Ghats shows how sharply rainfall falls from the windward coast to the rain shadow of the plateau.

Option A, an isobar, joins places of equal atmospheric pressure and is used on weather charts to locate depressions and anticyclones. Option C, an isotherm, joins places of equal temperature and is used on temperature maps. Option D, an isohaline, joins places of equal salinity and belongs to the study of the oceans. All four terms carry the Greek prefix iso, meaning equal, and examiners rely on a candidate confusing them.

The correct answer is B, neither I nor II, which means that both the pairs given are correct and none of them is wrong. In the Koeppen classification as applied to India, the semi-arid steppe climate marked BShw covers parts of Punjab, Haryana, western Uttar Pradesh and the drier interior of the peninsula, where rainfall is low but not as low as in a true desert. The monsoon type with a dry summer, marked As, covers the Coromandel coast of Tamil Nadu, which stays dry in the south-west monsoon months and receives its rain from the retreating monsoon in winter.

Options A and C each reject one of the two correct pairs, and option D rejects both. The trap lies in expecting every statement in such a question to contain an error.