How does #"Avogadro's number"# relate to the atomic mass of #""^12C# isotope?
Suppose we isolated an atom of carbon-12. Would you agree that this atom has a definite and measurable mass?
I think you would agree this of that atom. If instead of 1 atom of carbon-12, I had exactly Avogadro's number of carbon-12 atoms, I would have a mass of 12 grams precisely. Avogadro's number (which you will certainly not need to memorize is approx.
If you look on the Periodic Table, the molar mass of carbon is 12.011 g. Can you account for this?