Q. Which Assam district has India's oldest oil refinery at Digboi?
Answer:
Tinsukia
Notes: Tinsukia district in Assam hosts the Digboi oil refinery, India's oldest refinery established during British rule. It covers 3,790 km² and was historically part of the Sutiya kingdom. The refinery began production in the early 20th century and is a significant industrial center in the region.