The correct answer is option 3: Hirakud Dam. The Hirakud Dam is located in the state of Odisha in India and is the longest dam in the country. It was built across the Mahanadi River and has a length of about 26 kilometers. The primary purpose of the Hirakud Dam is to control floods in the Mahanadi River and provide irrigation water for agriculture in the region. It also generates hydroelectric power, making it a multi-purpose dam.
Option 1: Bhakra Dam is a major dam located in the northern state of Himachal Pradesh. It is one of the tallest dams in India, but not the longest.
Option 2: Nagarjuna Sagar Dam is located in the state of Telangana. It is one of the largest masonry dams in the world, but again, not the longest.
Option 4: Kosi Dam is located in the state of Bihar. It is an embankment dam, primarily built for flood control and irrigation. However, it is not the longest dam in India.
Therefore, the correct answer is option 3: Hirakud Dam.