The correct answer is: a) Alluvial soils.
Alluvial soils are the dominant soil type in Mizoram. They are formed by the deposition of sediments from rivers and streams. Alluvial soils are typically rich in nutrients and organic matter, and they are well-drained. This makes them ideal for agriculture.
Laterite soils are formed in tropical and subtropical climates. They are rich in iron and aluminum oxides, and they are typically red or yellow in color. Laterite soils are not very fertile, and they are prone to erosion.
Black cotton soils are formed in semi-arid climates. They are rich in organic matter, and they are dark in color. Black cotton soils are very fertile, but they are also prone to waterlogging.
Desert soils are formed in arid climates. They are typically sandy or rocky, and they are low in nutrients. Desert soils are not very fertile, and they are prone to erosion.