Trade winds are caused by the

Answer: (c) In flowing movement of air along the earth's surface towards the equator

Air flows from the subtropical highs towards the equatorial low — the trade winds.

The idea

A horizontal pressure difference starts air moving from higher towards lower pressure. In the tropics, surface air travels from subtropical highs towards the equatorial low. Rotation turns that flow into the easterly trade winds. The driving force and the turning effect are different parts of the explanation.

Strong tropical heating encourages ascent → Equatorial low pressure develops → Subtropical descending air forms highs → Surface air flows towards the equatorial low → Rotation bends it into NE and SE trades

Why the others are wrong

(b) Rotation deflects them but doesn’t cause them.

The trap

Rotation explains their direction, not their existence.

Elimination technique

Rotation changes the direction of existing motion; it is not the pressure-gradient force that starts the flow. Of the options, the equatorward surface inflow identifies the trade-wind branch itself.

Also know

The trade winds converge near the ITCZ, where rising moist air commonly brings rain. They blow from the north-east in the north and south-east in the south. Westerlies move poleward from the subtropical highs instead. The ITCZ shifts seasonally, so the ideal latitude belts are not fixed on the ground.