The correct answer is Patna.
Patna is the capital of Bihar and the largest city in the state. It is located on the banks of the Ganges River and is a major transportation hub. Patna is also a major industrial center, with industries such as textiles, engineering, and pharmaceuticals.
Muzaffarpur is the second largest city in Bihar and is located in the north-central part of the state. It is a major agricultural center and is also home to a number of industries, including textiles, engineering, and food processing.
Bhagalpur is the third largest city in Bihar and is located in the south-central part of the state. It is a major industrial center, with industries such as textiles, engineering, and chemicals.
Gaya is the fourth largest city in Bihar and is located in the south-eastern part of the state. It is a major religious center and is also home to a number of industries, including textiles, engineering, and food processing.
In conclusion, Patna is the largest industrial hub in Bihar. It is a major transportation hub and is home to a number of industries, including textiles, engineering, and pharmaceuticals.