Answer:
The correct answer is increase in temperature.
Step-by-step explanation:
During heating of the iron ore with the hydrogen gas at high temperature, the production of water and element iron takes place. High temperature is one of the essential condition for this chemical reaction to take place.
The more the temperature is, the more will be the amount of the production of iron, this is due to the presence of high temperature, which is one of the mediating force for the production of iron. Therefore, an increase in temperature will produce a greater amount of iron.