The diffusion of iron in crystalline and metamorphic rocks results in soil developing ______ colour.

The correct answer is (C) Reddish

Explanation:
● The diffusion (oxidation) of iron in crystalline and metamorphic rocks leads to the formation of iron oxides.
● Iron oxides such as hematite impart a reddish colour to the soil.
● Hence, soils derived from iron-rich crystalline and metamorphic rocks commonly appear red.

Information Booster:
● Red soils are widespread in parts of Tamil Nadu, Karnataka, Odisha, Chhattisgarh, and Andhra Pradesh.
● The red colour is mainly due to the presence of ferric oxide (Fe₂O₃).
● These soils are generally porous and friable in nature.
● Red soils are usually deficient in nitrogen, phosphorus, and humus.
● They are suitable for crops like millets, pulses, groundnut, and cotton with proper irrigation.

Additional Knowledge:
● Blackish soils are rich in humus or formed from basalt (regur soil).
● Bluish soils are associated with waterlogged or reduced conditions.
● Greenish soils are rare and linked with specific mineral compositions, not iron oxidation.