To solve this question, the user needs to have knowledge about Thorium and its deposits in India.

Thorium is a radioactive element that is widely distributed in nature. India has the world's largest deposit of thorium.

Now, let's go through each option and explain why it is right or wrong:

A. Karnataka: This option is incorrect. Although Karnataka has some of the richest mineral ores in the country, it does not have the largest deposit of thorium.

B. Andhra Pradesh: This option is incorrect. Andhra Pradesh is known for its large reserves of bauxite, mica, and coal, but it does not have the largest deposit of thorium in India.

C. Kerala: This option is correct. Kerala has the world's largest deposit of thorium. The rare earth minerals found in Kerala's coastal sands are estimated to be 30% of the world's reserves.

D. Maharashtra: This option is incorrect. Maharashtra has significant reserves of iron ore, coal, manganese, bauxite, and limestone, but it does not have the largest deposit of thorium.

The Answer is: C. Kerala