The molar mass of an element is the mass of one

Explanation:

The molar mass of an element is its atomic mass, i.e.  the mass in grams of one mole of atoms of the element.

Remember 1 mol is approximately 6.022 × 10²³.

So, 1 mol of atoms is 6.022 × 10²³ atoms.

The molar mass is an average: it is the weighted average mass of the natural isotopes of the element, taking into account their relative abundance.

For example, the molar mass or atomic mass of carbon is 12,0107 g/mol, instead of 12.0000, becasue carbon exists in several forms (isotopes), and so the weighted average is not a whole number.