Answer : 4. "लौह-अयस्क"
Explanation :

1. Although Rajasthan is not rich in this mineral, the deposits available are of high quality (hematite and magnetite).

2. Most of the ore found in the form of hematite is found in small deposits which were mined uneconomically.

3. Some magnetites are also found at various places.

4. Iron ore in the state is found in the north-eastern and south-eastern parts of the state.