The climate of Bihar is best described as:

The correct answer is A, from north-east to south-west. The rain comes to Bihar with the Bay of Bengal branch of the south-west monsoon, which enters from the east and loses moisture as it moves inland. So Kishanganj, Araria and Purnia in the north-east are the wettest districts, the Champaran belt is well watered, and Gaya, Aurangabad and the Kaimur tract in the south-west receive the least and suffer drought most often.

Option B reverses the real pattern of the north, where the Himalayan foothills get more rain, not less. Option C, from west to east, is the pattern of the Ganga plain as a whole only if you read it the other way round: rainfall rises eastwards from Punjab towards Bengal. Option D is wrong because the difference across Bihar is large, from well over 1,500 millimetres in the north-east to around a thousand in the south-west. This gradient is the reason flood is a North Bihar problem and drought a South Bihar one.

The correct answer is A, Kishanganj. Kishanganj lies in the extreme north-east of the state, in the corner nearest the Darjeeling hills and the moist Bengal duars, and it is the first part of Bihar the monsoon current reaches. It is the wettest district of the state, and the neighbouring districts of Araria and Purnia come close behind it.

Option B, Gaya, in the south-west, is one of the driest and hottest districts and is a standard example of the drought-prone South Bihar plain. Option C, Aurangabad, lies next to Gaya in the same dry tract and depends on the Sone canal system for irrigation. Option D, Rohtas, is also in the south-west, in the Kaimur country, and is irrigated rather than well watered. The examiner's point is always the same contrast: wettest in the north-east, driest in the south-west.

The correct answer is B, the Bay of Bengal branch. This branch of the south-west monsoon strikes the Bengal coast, is deflected west by the Himalaya and moves up the Ganga plain, reaching Bihar in the second week of June. Because the current travels from east to west across the state, the north-east gets the rain first and most heavily, and the south-west gets the least.

Option A, the Arabian Sea branch, waters the west coast, the Western Ghats and central and north-west India, and only a weakened remnant of it reaches the eastern plain. Option C, the retreating monsoon of October and November, gives rain to the Tamil Nadu coast, not to Bihar, where those months are dry and clear. Option D, western disturbances, are winter depressions from the Mediterranean that bring a little rain to north-west India and sometimes light showers to Bihar in January, useful for the rabi crop but a very small part of the annual total.

The correct answer is B, three. For agricultural planning Bihar is divided into Zone I, the north-west alluvial plain, Zone II, the north-east alluvial plain, and Zone III, the South Bihar alluvial plain, which is further subdivided into III A and III B. The division follows the two things that actually differ across the state: the Ganga, which separates north from south, and the rainfall gradient, which separates the wet north-east from the drier north-west and south.

Option A, two, would be right only if the Ganga were the sole basis of the division. Option C, five, and option D, seven, are the kinds of numbers used for other states and for the national scheme of agro-climatic regions, in which Bihar falls in the middle Gangetic plain region. For the exam, hold on to three main zones with the southern one split in two, and remember that Zone II, the north-east, is the wettest and the most flood-affected.

The correct answer is A, calcareous, that is rich in lime. The rivers of North Bihar come down from the young Himalaya and spread fresh silt over the plain at every flood, and that silt carries a high proportion of lime. The soil is therefore light in texture, pale, low in nitrogen and organic matter, and renewed each year, which is why it responds so well to manure and to balanced fertiliser.

Option B, lateritic soil, forms under heavy rain on old rock with leaching, and in Bihar it occurs only in patches on the Kaimur fringe and in Jamui, Banka and Munger. Option C, black and highly clayey, describes the karail soil of the Son valley and the tal soil of the Mokama belt, both of them South Bihar types. Option D is wrong as a general statement: saline and alkaline usar patches do occur in canal commands, but they are local, not a character of the whole belt. The clean pairing to remember is newer alluvium with calcareous North Bihar and older alluvium with clayey South Bihar.