Which of the following determines the atomic number of an element?

• A. The total number of electrons in all energy levels
• B. The number of neutrons in the nucleus
• C. The number of protons in the nucleus
• D. The sum of protons and neutrons in the nucleus

Answer: (C)

Verified step by step guidance

1. Understand that the atomic number of an element is a fundamental property that uniquely identifies the element.
2. Recall that the atomic number is defined as the number of protons in the nucleus of an atom.
3. Recognize that while electrons and neutrons are important subatomic particles, they do not determine the atomic number: electrons can vary in ions, and neutrons vary in isotopes.
4. Note that the total number of electrons in all energy levels equals the atomic number only in a neutral atom, but this is not the defining property of the element.
5. Conclude that the correct determinant of the atomic number is the number of protons in the nucleus.