The correct answer is: c) Western Ghats foothills.
Limestone deposits are extensively found in the Western Ghats foothills of Tamil Nadu. The Western Ghats are a mountain range that runs along the western coast of India. The foothills of the Western Ghats are a region of rolling hills and valleys. The climate in the foothills is tropical, with hot, humid summers and cool, dry winters. The soil in the foothills is rich in limestone, which is a type of rock that is formed from the remains of marine organisms. Limestone is used in a variety of industries, including construction, manufacturing, and agriculture.
The other options are incorrect. Option a) is incorrect because the northern districts of Tamil Nadu are not known for their limestone deposits. Option b) is incorrect because the southern districts of Tamil Nadu are not known for their limestone deposits. Option d) is incorrect because the coastal regions of Tamil Nadu are not known for their limestone deposits.