The chemical standard for the quantity of a mole is based on which substance? a. hydrogen-1 b. helium-2 c. oxygen-16 d. carbon-12

The chemical standard used as a basis for the quantity of a mole is the carbon-12. Thus, the answer is letter D. By definition a mole is the number of atoms that would compose 12 g of the carbon-12. The reason for choosing such is that carbon is plentiful and not too hard to make isotropically pure.