The atomic number of an element is:. 1. the submit answer button. 2. the number of neutrons in the nucleus of one atom. 3. the number of protons in the nucleus of one atom. 4. the total number of particles in the nucleus of one atom. the mass of one atom, in atomic mass units (amu). 5. the number of electrons in the nucleus of one atom

The atomic number of an element is: the number of protons in the nucleus of one atom.

Explanation:

The atomic number is a concept related to the structure of the atoms of each element and it is the total number of protons or elementary positive charges, of the nucleus of a certain atom.

Option 3==> the number of protons in the nucleus of one atom.

Explanation:

In an atom, atomic number is the number of proton in the nucleus. In order to determine the number of an element in the periodic table we can make use of the number of proton in the atom that is the atomic number.

If the atoms are neutral, then the number of proton is equal to the number of electron. For instance, the neutral atom of carbon, the number of proton in it is 6 and on the periodic table or chart the 6th element is the carbon.

it is the most commonly accepted one