Oil refinery is located at which place in Bihar state?

Barauni
Singhbhum
Rudrasagar
Ranchi

The correct answer is A. Barauni.

Barauni is a city and a notified area committee in Begusarai district in the Indian state of Bihar. It is located on the banks of the Ganges River, about 120 kilometres (75 mi) north of Patna, the state capital. The city is known for its oil refinery, which is one of the largest in India.

The other options are incorrect. Singhbhum is a district in Jharkhand state. Rudrasagar is a town in Ranchi district in Jharkhand state. Ranchi is the capital of Jharkhand state.