The Farakka Barrage was built in India with the primary purpose of checking the water flowing into Bangladesh. The barrage diverts a portion of the Ganges River flow into the Hooghly River, reducing the water flow into Bangladesh during the dry season. This diversion aimed to manage water availability for irrigation and navigation purposes in India.

The option 2, checking silting of Kolkata Port is incorrect. One of the secondary purposes of the Farakka Barrage was to increase water flow in the Hooghly River, which would help to prevent silting of the Kolkata Port. The barrage was expected to maintain a minimum depth for navigation in the river.

Option 3, preventing erosion of Kolkata Port, is also incorrect. The Farakka Barrage was not built to prevent erosion of the Kolkata Port.

Option 4, facilitating navigation in the Ganga River is the correct answer. The Farakka Barrage was primarily built to regulate water flow into Bangladesh and support irrigation, not for navigation purposes. Alert - Correct answer should be 3.