The correct answer is Purnia.
Purnia is a district in the Indian state of Bihar. It is located in the north-eastern part of the state and is bordered by the districts of Katihar to the north, Araria to the east, Saharsa to the south, and Bhagalpur to the west. The district has a population of over 5 million people and is the third most populous district in Bihar.
Purnia is known for its goat population. The district is home to over 2 million goats, which are used for meat, milk, and wool. Goat farming is a major source of income for many people in the district.
The other options are incorrect. Gaya is a district in the south-central part of Bihar. Muzaffarpur is a district in the north-central part of Bihar. Bhagalpur is a district in the south-western part of Bihar. These districts are not known for their goat population.