Correct Answer - Option 4 : Blast furnace slag
Explanation:
Slag Cement: Slag cement is a hydraulic cement formed when granulated blast furnace slag (GGBFS) is ground to suitable fineness and is used to replace a portion of portland cement.
Blast furnace slag: It is a recovered industrial by-product of an iron blast furnace.
Fly ash: Fly ash is a byproduct of burning pulverized coal in electric power generating plants.
Ferro alloy: An alloy of iron with some element other than carbon, used to introduce the element in the manufacture of steel.