Step 1: Understand the location of Zuari River.
The Zuari River is the largest river in the state of Goa, India. It is a tidal river that originates in the Western Ghats and flows into the Arabian Sea [citation:7]. The Zuari and Mandovi rivers form an estuarine system and are connected by the Cumbarjua Canal [citation:7].
Step 2: Identify the port at Zuari Estuary.
The waters of the Mandovi and Zuari both flush out into the Arabian Sea at Cabo Aguada, a common point forming the **Mormugao harbour** [citation:7]. The port city of **Vasco da Gama, Goa lies on the mouth of the Zuari River** [citation:7].
Mormugao port is situated at the entrance of the Zuari estuary and is a natural harbour in Goa [citation:3]. It gained significance after its remodelling in 1961 to handle iron-ore exports [citation:3].
Step 3: Analysis of each option.
(A) New Mangalore: Incorrect. New Mangalore port is located in Karnataka, on the banks of the Netravati and Gurupura rivers, not the Zuari estuary.
(B) Kochchi: Incorrect. Kochi (Cochin) port is located in Kerala, on the estuary of the Periyar River, not the Zuari.
(C) Marmagao:Correct.} Marmagao port is situated at the entrance of the Zuari estuary in Goa. It is a natural harbour developed primarily for iron-ore exports [citation:3][citation:7].
(D) Ennore: Incorrect. Ennore port (now Kamarajar Port) is located in Tamil Nadu, north of Chennai, and has no connection to the Zuari estuary.
Step 4: Conclusion.
Marmagao port in Goa is the only major port situated at the Zuari estuary. It handles significant iron-ore exports and its hinterland includes Karnataka, Goa, and Southern Maharashtra [citation:3].
Final Answer:} (C) Marmagao
