Find the odd one out from the given alternatives:

Correct — D.
Rule: three of the four are soil types; one is a rock type.

Alluvial, black and red are classes of soil.

Igneous rock is a class of rock, formed when molten magma or lava cools and hardens → option (d).

Why the others are wrong

• (a)
  Alluvial Soil — Alluvial soil is a soil, laid down by rivers as silt and sand. It belongs with black and red soil.
• (b)
  Black Soil — Black soil forms from weathered basalt, an igneous rock, but it is itself a soil. Its link to lava does not move it into the rock group.
• (c)
  Red Soil — Red soil is a soil, its colour coming from iron. It groups with alluvial and black soil, not with rocks.

Soil and rock are stages, not rivals: rock weathers, mixes with organic matter and becomes soil. The rock a soil forms from is its parent material.

Black and red soil both trace back to igneous rock: black soil to the basalt of the Deccan lava region, red soil to crystalline rocks of the Deccan.

The options ask for a class, and igneous rock is the parent, not the product.

Key facts

• Rocks fall into three classes by origin: igneous, sedimentary and metamorphic.
• Igneous rock forms when magma or lava cools and solidifies. Basalt and granite are examples.
• Black soil, also called regur, is typical of the basalt (Deccan trap) region.
• Alluvial soil is deposited by rivers and makes up the northern plains of India.

Common traps

• Picking Black Soil because it comes from lava: its parent rock is igneous, but black soil is still a soil.

No directly related past PYQ was found.