No, "mass number" and "molar mass" are not the same thing.
The mass number refers to the total number of protons and neutrons in the nucleus of an atom. It is often represented by the symbol 'A' and is used to identify isotopes of an element. For example, carbon-12 and carbon-14 have different mass numbers (12 and 14, respectively), indicating that they have different numbers of neutrons.
On the other hand, molar mass is a concept used in chemistry and refers to the mass of one mole of a substance. It is expressed in grams per mole (g/mol) and is calculated by summing the atomic masses of all the atoms in a chemical formula. The molar mass is used to convert between the mass of a substance and the number of moles present. It is an important quantity in stoichiometric calculations and is also used to determine the mass or amount of a substance in a given sample.
In summary, while mass number relates to the composition of a specific isotope, molar mass is a broader concept that pertains to the mass of a substance on a per-mole basis.