The correct answer is option 1: to save Kolkata port. The Farakka Barrage, which was commissioned in 1975, was built with the primary aim of maintaining a minimum navigable depth in the Hooghly River, thus saving the Kolkata port from experiencing the adverse effects of siltation. The barrage regulates the amount of water flowing downstream, preventing excessive silt buildup and ensuring a steady flow of water for navigation purposes. This is crucial for maintaining the port`s functionality and enabling the movement of cargo ships and vessels. Additionally, the Farakka Barrage also has several secondary purposes, such as controlling floods and improving water availability in areas surrounding the Hooghly River. However, the primary objective of its construction was to save the Kolkata port.