For which element would you expect isotope effects to be of the greatest importance in CHEMICAL processes?

Question

a.H
b.He
c.Li
d.B

This problem could be interpreted many different ways and come up with different answers, I suppose. In the context of number of compounds formed, I would go with H since there are so many different H compounds. In the same vein, the ratio of the mass number for H is 1:2:3 whereas He is 3:4, Li is 6:7 and B is 10:11. So we would notice the greatest effect for compounds containing H.