Whether a river forms a delta or an estuary at its mouth depends on how much sediment it carries and how strongly the sea disperses that sediment. A delta forms where a river deposits large amounts of silt faster than waves and tides can carry it away, building up a fan of low, fertile land. An estuary forms where a swift river meets strong tidal action that flushes the sediment out to sea.

The Godavari — the largest peninsular river of India — rises at Trimbak near Nashik in the Western Ghats and flows eastward across the Deccan Plateau. On this long journey it gathers a heavy sediment load, and on reaching the Bay of Bengal in Andhra Pradesh it spreads out into a large, well-developed delta on the eastern coastal plains. This delta is one of India's most productive rice-growing regions, which is why the Godavari is the correct answer.

The other rivers do not fit:

• Tapi and Narmada both flow westward through rift valleys and empty into the Arabian Sea, forming estuaries, not deltas — their fast flow and the Arabian Sea's tides prevent sediment from settling. They are also on the western side, not the eastern coastal plains.
• The Ganga does form a delta (the Sundarbans), but the question points to a river of the eastern coastal plains of peninsular India; the Ganga delta lies in the Gangetic plains of West Bengal and Bangladesh. Among the choices, the Godavari is the river that specifically builds a delta along the eastern coastal plains.