What is the atomic number of a chemical element?

The number of neutrons in the atom's nucleus
99
The number of atoms
116
The number of protons in the atomic nucleus
352
The number of electrons in the atomic nucleus
117
The atomic number or proton number of a chemical element is the number of protons found in the nucleus of an atom. It is identical to the charge number of the nucleus. The atomic number uniquely identifies a chemical element.
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