RAS question
Red soils in Rajasthan are found mainly in which districts, and what gives them their characteristic colour?
Correct answer: (B) Dungarpur, Banswara, Chittorgarh, Udaipur; iron oxide (Fe₂O₃).
In Rajasthan, red soils are found mainly in Dungarpur, Banswara, Chittorgarh and Udaipur, and their red colour comes from diffused iron oxide in crystalline and metamorphic rocks.
Explanation
Red soils in Rajasthan are concentrated in the southern districts of Dungarpur, Banswara, Chittorgarh and Udaipur. The key clue is the parent material: these soils occur on gneisses and schists, and NCERT.App notes that red and yellow soils develop on crystalline igneous and metamorphic rocks such as granite and gneiss. Their colour is not a surface stain or organic effect; it comes from diffused iron oxides in those rocks, with Fe2O3 or haematite as the colouring agent. These soils are well drained, generally poor in nitrogen and phosphorus, and respond to irrigation for crops such as maize, jowar, groundnut and cotton.
Why the other options are wrong
- (A) Bikaner and Jaisalmer point to western Rajasthan's arid, sandy soils, where calcium carbonate kankar is associated with desert soils rather than the iron-oxide redness of southern red soils.
- (C) Kota, Bundi and Jhalawar belong to the black cotton soil belt, whose dark colour is linked to titaniferous magnetite and humus, not manganese oxide.
- (D) Sikar, Jhunjhunu and Churu have semi-arid sandy-loam conditions with low humus, so humus accumulation cannot explain a red-soil zone there.
Concept
This tests soil classification in Rajasthan through distribution, parent rock and colour chemistry. RAS repeats this theme because district mapping and soil properties are a compact way to connect physical geography with agriculture.