The correct answer is A. Arwal.
Arwal district has the lowest population density as per Census 2011. The population density of Arwal district is 394 per square kilometer. The population density of Madhubani district is 829 per square kilometer. The population density of Saran district is 1,024 per square kilometer. The population density of Kaimur district is 665 per square kilometer.
Arwal district is a district in the state of Bihar, India. It is located in the southern part of the state and is bounded by the districts of Rohtas to the north, Jehanabad to the east, Gaya to the south, and Nalanda to the west. The district headquarters is the town of Arwal.
The district has a total area of 2,324 square kilometers. The population of the district as per the 2011 census is 1,025,943. The sex ratio of the district is 911 females per 1,000 males. The literacy rate of the district is 62.9%.
The main occupation of the people of the district is agriculture. The main crops grown in the district are rice, wheat, maize, and pulses. The district is also known for its production of milk and milk products.
The district has a number of historical and religious places. The most famous of these is the tomb of Sher Shah Suri, the founder of the Sur Empire. The district also has a number of temples and mosques.
The district is well-connected by road and rail. The nearest airport is the Patna Airport.