Answer : 4. "आयरन "
Explanation :

1. Hematite is an ore of iron. It is commonly found in stones and soil. The largest quantity of iron in the earth is found in the form of hematite.

2. The chemical formula of hematite is Fe2O3. It is a heavy and relatively hard oxide mineral.

  3. Its colour ranges from black to steel or silver-grey, grey to brown or reddish.

4. Hematite is used in the production of iron. It is an important mineral that is found in many countries around the world.