Assertion (A): The monsoonal rainfall decreases as one goes towards the west and northwest in the Ganga plain. Reason (R): The moisture bearing monsoonal winds go higher up as one moves up in the Ganga plain.

Answer: (c) A is true, but R is false

Rain does fall off westwards, but because the winds lose moisture as they travel inland, not because they rise higher.

The idea

Rain needs both moisture and a way to lift the air. Moist winds generally lose water as they travel and rain over land. A broad plain does not act like a mountain barrier, so a westward rainfall decline must not be explained by continuous steep ascent.

Bay branch enters eastern India → Rain falls along its inland path → Moisture supply generally decreases westward → Distance from the Bay increases → The north-western plain receives less monsoon rain

Why the others are wrong

(a) Accepts R.

(b) Accepts R.

(d) Rejects the westward decline.

The trap

R sounds like an orographic reason, but the Ganga plain is flat.

Elimination technique

The assertion gives the broad plain rainfall gradient. The reason treats the plain as a rising mountain slope; that is not the mechanism. With A true and R false, retain (c).

Also know

Hill slopes can interrupt this broad pattern through orographic lifting. The Himalayan foothills may be wetter than nearby plains, while the Deccan has a separate rain-shadow pattern. Winter rain in the north-west comes from western disturbances rather than this summer moisture path.