The answer is c. because you have to increase concentration of h2
Hi :)
The bottom number tells you how many protons you have in the nucleus of this element.
In Krypton-84, this means that you have 84 nucleons, where 36 of these are protons, and the remaining 48 are neutrons.
Hope this helps :)
I believe it is D. because stoichiometry allows people to determine how much reactant is consumed in a chemical reaction.