Lothal was the port through which the Harappans traded with West Asia — option 2.

The site. Lothal lies in the Bhal region of Gujarat, near the Gulf of Khambhat, and was excavated by S. R. Rao from 1955. Its most striking feature is a large brick-lined basin, about 214 metres by 36, generally identified as a dockyard — which would make it the earliest known dock in the world — with an inlet channel connected to the Sabarmati and a spillway to regulate the water level.

The trade itself. Mesopotamian records speak of trade with Meluhha, generally identified with the Indus region, and with the intermediate stations of Dilmun (Bahrain) and Magan (Oman). Harappan seals, weights, carnelian beads and etched beads have been found at Ur, Kish and Susa. The exports were beads, ivory, timber, cotton and copper; the imports included silver, tin and precious stones.

The other sites named. Ropar (Rupnagar) in Punjab, on the Sutlej, was the first Harappan site excavated after independence, and is noted for a dog buried with a human. Kalibangan in Rajasthan, on the dry Ghaggar, is famous for the world’s earliest ploughed field and for its fire altars. Both are inland sites, and neither could have carried on maritime trade — which is the point of the question.

Other Harappan ports : Sutkagendor on the Makran coast, Balakot, Allahdino, and Dholavira in the Rann of Kachchh.

Hence, the answer is Lothal.