The number of which subatomic particle designates the atomic number of an element? select one:

The atomic number is determined by the number of protons in the atom. 

Neutrons can vary the mass of atoms of the same element; atoms of the same element with the different atomic masses are called isotopes. 

Electrons do not contribute a meaningful amount of mass to an atom, and only vary the charge of the atom. A charge atom is an ion.

The number of protons always equals the atomic number of an element.

Ibelieve it is b. proton.hope my answer has you : )

The molar mass of a substance is defined as the mass of 1 mol of that substance, expressed in grams per mole, and is equal to the mass of 6.022 × 10 23 atoms, molecules, or formula units of that substance.