I think it is enzymes.Inside our body most of the chemical reactions are speeds up by enzymes.These enzymes decreases the minimum energy that is required for the reaction to happen. ;-]. Actually it works like a catalyst.
The answer lies in the stoichiometry of the reaction. If u look at the number BEFORE the reagent u will see the ratios of the reagents.
The answer should be 0.5 because 6/12 is 0.5. It gives u the key equation
