The correct answer is (b) Salem.
Lignite mines are primarily located in the Salem district of Tamil Nadu. The Salem lignite field is one of the largest in India, with reserves of over 2 billion tonnes. The field is located in the northern part of the district, near the town of Salem. The lignite is used to generate electricity at the Salem Thermal Power Station.
The other options are incorrect. Cuddalore is a district in the northern part of Tamil Nadu. The district is known for its production of sugar and rice. Tirunelveli is a district in the southern part of Tamil Nadu. The district is known for its production of tea and coffee. Coimbatore is a district in the western part of Tamil Nadu. The district is known for its production of textiles and engineering goods.