The black cotton soil of India has been formed due to the weathering of

• Black Soil:
-​The parent material for most of the black soil is the volcanic rocks that were formed in the Deccan Plateau (Deccan and the Rajmahal trap). Hence, option 2 is the correct answer.
-A typical black soil is highly argillaceous [Geology (of rocks or sediment) consisting of or containing clay] with a large clay factor, 62 per cent or more.
-In general, black soils of uplands are of low fertility while those in the valleys are very fertile.
-The black colour is due to the presence of a small proportion of titaniferous magnetite or iron and black constituents of the parent rock.
-The black soil is highly retentive of moisture. It swells greatly on accumulating moisture. Strenuous effort is required to work on such soil in the rainy season as it gets very sticky.