A delta is a triangular landform built up where a river deposits its sediment load as it slows down on entering the sea. Deltas form best on gently sloping coasts where the river carries a large sediment load and tidal/wave action is not strong enough to sweep it away.

Among the given rivers, the Godavari is the one that forms a delta along the eastern coastal plains:

• It rises in the Western Ghats near Nashik (Maharashtra) and flows eastward across the Deccan Plateau.
• It empties into the Bay of Bengal in Andhra Pradesh, where it deposits sediment to build one of the largest and most fertile deltas in India, famous for extensive rice cultivation.

Contrast this with the peninsular rivers of the west coast:

• Narmada and Tapi both flow westward into the Arabian Sea and form estuaries, not deltas. They run through rift valleys, carry relatively little sediment, and the strong tidal action of the west coast flushes sediment out to sea, preventing delta formation.

The Ganga does form a very large delta (the Sundarbans), also on the eastern side, so it is a plausible-sounding choice. However, the question asks for a single river that forms a delta on the eastern coastal plains, and the Godavari is the intended answer as an east-flowing peninsular river building its delta directly along the eastern coast; the Ganga is a Himalayan river of northern/eastern India rather than a river of the peninsular eastern coastal plains being referenced here.