Assertion (A): Ganga Plain is the most densely populated part of India. Reason (R): Ganga is the most harnessed river of India.

Answer: (b) Both A and R are individually true but R is not the correct explanation of A.

Both are true, but density comes from fertile alluvium and long settlement, not from dams.

The idea

A settlement pattern needs a cause, not just another fact about the same region. Fertile land, water, farming and transport together help explain dense plains settlement. For assertion–reason questions, test each proposition first and then ask whether the reason actually explains the assertion.

Alluvium builds a plain → Level land is easier to cultivate → Water supports intensive farming → Food and markets support settlement → Transport links connect towns → Dense settlement develops over generations

Why the others are wrong

(a) Treats river harnessing as the reason for density.

(c) The key accepts R as true.

(d) A is true.

The trap

R is true and sounds connected, but it is not the cause.

Also know

The Ganga plain receives Himalayan tributaries such as Ghaghara, Gandak and Kosi, while the Yamuna system also drains parts of the plateau. The Brahmaputra valley and coastal deltas are other fertile alluvial landscapes. River engineering can support irrigation and transport, but it is not the sole measure of settlement potential.