The answer is: both choices a and b.
The base SI unit for molar mass is kg/mol, but chemist more use g/mol (gram per mole).
For example, the molar mass of fluorine is 38.00 g/mol.
M(F₂) = 2 · Ar(F) · g/mol.
M(F₂) = 2 · 19.00 · g/mol.
M(F₂) = 38.00 g/mol.
Molar mass M represent the mass of a substance (in this example molecule of florine) divided by the amount of substance.
Ar is the atomic weight of a chemical element (in this example fluorine).
