The port of Muziris, an important center of ancient trade, is believed to be located in modern-day:

The correct answer is: a) Kerala.

Muziris was an ancient port city on the Malabar Coast of India. It was an important center of trade between India and the Roman Empire. The city was destroyed by a tidal wave in the 14th century.

The port of Muziris is believed to be located in modern-day Pattanam, Kerala. Pattanam is a small village on the banks of the Periyar River. Archaeological excavations at Pattanam have revealed evidence of a thriving port city dating back to the 1st century BC.

The other options are incorrect. Tamil Nadu is a state in southern India. Andhra Pradesh is a state in southern India. Karnataka is a state in southern India.