UPSC Prelims 2010 Q91: Geography – Indian Agriculture & Land Use
When you travel in certain parts of India, you will notice red soil. What is the main reason for
this colour?
- (a) Abundance of magnesium
- (b) Accumulated humus
- (c) Presence of ferric oxides
- (d) Abundance of phosphates
Answer: (c) Presence of ferric oxides
Explanation
Why some Indian soils appear red
Red soil, common in parts of peninsular India, owes its colour to a specific mineral compound.
| Option | Verdict | Reason |
|---|---|---|
| (a) Abundance of magnesium | Incorrect | Magnesium is not the colour-determining factor in red soils |
| (b) Accumulated humus | Incorrect | Humus accumulation is associated with dark, fertile soils, not red colouration |
| (c) Presence of ferric oxides | Correct | Red soil's characteristic colour comes from the presence of ferric oxides (iron oxide), formed through the weathering of iron-rich rocks under specific climatic conditions |
| (d) Abundance of phosphates | Incorrect | Phosphates are not responsible for this red colouration |
Red soil basics:
| Point | Detail |
|---|---|
| Colour cause | Ferric oxides (iron oxide) |
| Formation | Weathering of iron-rich crystalline rocks |
| Region | Parts of peninsular India (Tamil Nadu, Karnataka, Odisha, etc.) |
Answer: (c) Presence of ferric oxides.
Why each option is right or wrong
- (a) Incorrect. Magnesium abundance is not the colour-determining mineral here.
- (b) Incorrect. Humus accumulation produces dark soils, not red colouration.
- (c) CORRECT. Ferric oxides (iron oxide), from weathered iron-rich rocks, give red soil its characteristic colour.
- (d) Incorrect. Phosphate abundance is unrelated to this specific red colouration.
Key point
Red soil's colour comes from FERRIC OXIDES (iron oxide), formed through the weathering of iron-rich rocks — not from magnesium, humus, or phosphates.
Remember
India's red soil owes its colour to the presence of ferric oxides (iron oxide), from weathered iron-rich rocks.
Common mistakes
- Confusing humus-related dark soils with iron-oxide-related red soils.
- Not knowing ferric oxide as the specific colour-causing compound in red soil.
- Attributing soil colour to unrelated minerals like magnesium or phosphates.
Exam tip
Red soil = ferric oxides (iron oxide) from weathered rock. Black soil = humus/basalt. Keep soil-colour causes distinct.
Sources
- NCERT Class XI Geography — India: Physical Environment — Soils
- National Bureau of Soil Survey and Land Use Planning — Soils of India