Which option is not related to the Northern Plains?

Correct answer: Coral island

Direct answer: Option D, coral island. The Northern Plains are broad level lands formed mainly by deposits brought by Himalayan rivers such as the Indus, Ganga and Brahmaputra systems. Their important features include fertile alluvial soil, river deposits and generally flat relief. A coral island, however, is an island built by coral organisms in warm, shallow marine water. It is not a feature of the river-made Northern Plains. Option A is related because alluvial soil is deposited by rivers and supports farming. Option B is related because river deposits form the plains. Option C is related because the plains have very gentle, level relief. Option D is correct because it belongs to a marine island environment, not an alluvial plain. Memory cue: “alluvium means river deposit”; “coral means sea island.”