RAS question
Red soil in India is formed by the weathering of:
Correct answer: (D) Crystalline and metamorphic rocks like granite and gneiss.
Red soil in India is formed by the weathering of crystalline and metamorphic rocks, especially rocks such as granite and gneiss.
Explanation
Red soil is linked to the weathering of crystalline and metamorphic parent rocks, with the key examples being granite and gneiss. NCERT explains that red soil develops on crystalline igneous rocks and gets its reddish colour from iron in crystalline and metamorphic rocks. This is why option D fits the formation process, while the colour is not a separate parent-material clue: it comes from iron oxide, specifically hematite. The soil is associated with parts of Tamil Nadu, Karnataka, Andhra Pradesh, Madhya Pradesh, Jharkhand and Odisha, covers about 10% of India, and is generally poor in nitrogen, phosphorus and humus but responds well to fertilisers.
Why the other options are wrong
- (A) Sandstone only is too narrow because the stated formation is from crystalline and metamorphic rocks, not a single sedimentary parent rock.
- (B) Limestone is not the parent material identified for red soil here; its weathering is associated with different soil formation.
- (C) Basaltic lava flows are the classic parent material for black soil, so choosing basalt confuses red soil with black soil.
Concept
This tests the Indian geography concept of soil formation through parent material, weathering and mineral content. It recurs in RAS because soil questions often ask candidates to connect colour, parent rock, fertility and regional distribution rather than memorise soil names in isolation.