What is the biggest physical advantage of the Northern Plains formed by river deposits?

Correct answer: Fertile and flat agricultural land

The Northern Plains were built by layers of alluvium deposited by rivers over a long period. Alluvial deposits usually contain fine particles and nutrients brought from the upper river basins. Because the land is also broad and level, it is comparatively easy to cultivate, irrigate, transport goods, and establish settlements. These combined physical features make the plains one of India’s major agricultural regions. The benefit asked here is the agricultural value of fertile, flat land.

Option B is correct because it states the main advantage created by river deposits: fertile and level agricultural land. Very high peaks belong to mountainous regions, coral reefs are marine formations, and volcanic craters are associated with volcanic activity. None of those describes the principal physical benefit of the alluvial Northern Plains. The answer follows directly from linking alluvium with fertility and plains with ease of cultivation.