Which river does not flow into the Arabian Sea but drains into the Bay of Bengal?

Correct answer: Mahanadi

Indian rivers drain mainly toward either the Arabian Sea or the Bay of Bengal. The direction depends on the slope of the land and the river basin. Tapi, Mahi, and Sabarmati flow generally westward and reach the Arabian Sea. Mahanadi, in contrast, flows eastward across central and eastern India before reaching the Bay of Bengal. Identifying the river mouth therefore distinguishes the correct option.

Mahanadi rises in the highlands of present-day Chhattisgarh and flows through Odisha. It forms a delta near its mouth and empties into the Bay of Bengal. Tapi, Mahi, and Sabarmati are west-flowing rivers associated with the Arabian Sea drainage. Thus option D, Mahanadi, is the river that does not drain into the Arabian Sea. The question is about the final drainage basin, not merely the state through which a river passes.