The correct answer is: c) Karimganj
Karimganj district is one of the 33 districts of Assam, India. It is located in the southern part of the state and is bounded by the districts of Hailakandi to the north, Cachar to the east, Mizoram to the south, and Tripura to the west. The district has a population of over 2.5 million people and its headquarters is at Karimganj town.
Karimganj district is a major producer of limestone. The limestone reserves in the district are estimated to be over 1 billion tonnes. The limestone is used in the manufacture of cement, lime, and other building materials. The district also has a number of limestone mines.
The other options are incorrect because:
- Nagaon district is located in the central part of Assam and does not have significant limestone reserves.
- Dima Hasao district is located in the north-eastern part of Assam and does not have significant limestone reserves.
- Jorhat district is located in the upper Assam region and does not have significant limestone reserves.