The correct answer is: A. Kathua
Kathua district is the largest district in Jammu region, Jammu and Kashmir, India. It is located in the south-west of the state, bordering the Indian state of Punjab to the south and the Pakistani-administered territory of Azad Kashmir to the west. The district has a population of over 1.5 million people and its headquarters is the town of Kathua.
The district is divided into four tehsils: Kathua, Billawar, Hiranagar, and Bani. The main towns in the district are Kathua, Billawar, Hiranagar, Bani, and Basohli.
The district is home to a number of historical and religious sites, including the Raghunath Temple in Jammu, the Shri Mata Vaishno Devi Temple in Katra, and the Akhnoor Fort.
The district is also home to a number of natural attractions, including the Chenab River, the Pir Panjal Range, and the Bhaderwah Wildlife Sanctuary.
Kathua district is a popular tourist destination, and is known for its natural beauty, historical sites, and religious shrines.
The other options are incorrect because:
- Rajouri district is the second largest district in Jammu region, after Kathua district.
- Doda district is the third largest district in Jammu region, after Kathua and Rajouri districts.
- Reasi district is the fourth largest district in Jammu region, after Kathua, Rajouri, and Doda districts.