Assam has significant reserves of:

Coal
Iron ore
Bauxite
Limestone

The correct answer is: a) Coal.

Assam is one of the major coal producing states in India. The coal reserves in Assam are estimated to be around 30 billion tonnes. The coal in Assam is of high quality and is used in the power generation, steel, cement and fertilizer industries.

The other options are incorrect because:

  • Iron ore is not found in significant quantities in Assam.
  • Bauxite is a mineral used to produce aluminum. There are no significant bauxite reserves in Assam.
  • Limestone is a sedimentary rock that is used in the construction industry. There are no significant limestone reserves in Assam.

I hope this helps!