The correct answer is option 2: Marmagao.

Estuary refers to the area where a river meets the sea or an ocean. It is characterized by a mixture of saltwater and freshwater. Marmagao is a port located in the state of Goa, India, and it is situated on the estuary of the Zuari River. The Zuari River flows into the Arabian Sea, forming an estuary where Marmagao port is situated.

Option 1: Kandala is a port located in Gujarat, India. It is situated on the Gulf of Kutch, which is not an estuary but a gulf.

Option 3: Kolkata-Haldia is a complex of ports located in West Bengal, India. Kolkata port is situated on the Hooghly River, which is a distributary of the Ganges River. Haldia port is located downstream on the estuary of the Hooghly River.

Option 4: Tuticorin, also known as Thoothukudi, is a port located in Tamil Nadu, India. It is situated on the Gulf of Mannar, which is not an estuary but a small gulf.

In conclusion, Marmagao port, option 2, is