Answer : 1. "डिगबोई रिफाइनरी"
Explanation :

Digboi Refinery is considered India's first oil refinery. It was established in 1901 in Digboi, Assam. The refinery played a significant role in the early development of the oil industry in India. Digboi Refinery continues to be in operation, making it one of the oldest operating refineries in the world.