RAS question
Red soils are formed due to the decomposition of:
Correct answer: (B) Igneous and metamorphic rocks rich in iron.
Red soils are formed by the weathering of iron-bearing crystalline igneous and metamorphic rocks.
Explanation
Red soils come from the weathering of ancient crystalline and metamorphic rocks, especially where iron is present in the parent material. NCERT explains that red soil develops on crystalline igneous rocks in low-rainfall areas of the eastern and southern Deccan plateau, and that its reddish colour is due to the diffusion of iron in crystalline and metamorphic rocks. Iron-rich igneous and metamorphic rocks are therefore the parent material behind both the formation and colour of red soils. This parent-material link also fits the listed distribution: red and yellow soils occur in parts of Odisha, Chhattisgarh, southern parts of the middle Ganga plain, along the Western Ghats piedmont, and in southern Indian states such as Tamil Nadu, Karnataka and Andhra Pradesh.
Why the other options are wrong
- (A) Alluvial deposits produce alluvial soils, so they do not explain red soil formation from iron-bearing crystalline and metamorphic rocks.
- (C) Limestone is not the parent material identified for red soils; their formation depends on iron in crystalline igneous and metamorphic rocks.
- (D) Volcanic basalt is associated with black soils, whereas red soils are tied here to crystalline igneous and metamorphic rocks with iron.
Concept
This tests Indian soil types by parent material and colour, a recurring RAS geography theme because soil classification links physical geography with agriculture and regional distribution. Red soil questions often hinge on recognising iron as the cause of the red colour.