ANS:A - Increases the reducing potential of the gas.

In the blast furnace, the incorporation of water vapor in the blast has the effect of increasing the reducing potential of the gas. Water vapor (H2O) dissociates into hydrogen (H2) and oxygen (O2) at high temperatures inside the blast furnace. The hydrogen (H2) acts as a reducing agent, which reacts with the iron oxides present in the iron ore to produce metallic iron and water vapor. This increased reducing potential facilitates the reduction of iron oxides, leading to higher iron yield and improved efficiency of the blast furnace operation. Therefore, incorporating water vapor in the blast enhances the reducing potential of the gas, aiding in the reduction of iron oxides to produce iron.