Chennai is an artificial port — option 4.

The distinction being tested. A natural harbour is one where the coastline itself — a bay, a creek, an estuary or a lagoon — provides shelter from waves and wind, so ships can lie safely with little construction. An artificial harbour has no such shelter and must be created by building breakwaters, moles and dredged channels out into the open sea.

Why Chennai had to be built. The Coromandel coast runs almost straight north to south with no inlets, and it is exposed to heavy surf and to cyclones from the Bay of Bengal. Cargo was originally landed by surf boats from ships anchored offshore. An enclosed harbour was constructed from 1876 onwards, with long breakwaters and an entrance later moved to the north-east to reduce silting from the littoral drift — the same drift that still requires continual dredging today. Chennai is the oldest artificial harbour on the east coast and remains one of India’s major ports, handling containers, automobiles and general cargo.

The wider pattern. India’s west coast is indented, drowned and rocky, so it offers many natural harbours — Mumbai, Marmugao, Kochi, Mangaluru. The east coast is an emergent, straight coast of deltas and sand bars, so its ports — Chennai, Paradip, Tuticorin, Visakhapatnam’s outer harbour — generally needed engineering to create. Visakhapatnam is the notable east-coast exception, being sheltered in the mouth of the Meghadrigedda.

Hence, the answer is Chennai.