Which property determines the identity of an atom?

• A. The number of protons in the nucleus
• B. The number of electrons in the atom
• C. The number of neutrons in the nucleus
• D. The total mass of the atom

Answer: (A)

Verified step by step guidance

1. Understand that the identity of an atom is defined by its atomic number, which is the number of protons in its nucleus.
2. Recall that the atomic number uniquely identifies an element because each element has a different number of protons.
3. Note that the number of electrons can vary in ions, and the number of neutrons can vary in isotopes, but these do not change the element's identity.
4. Recognize that the total mass of the atom depends on both protons and neutrons, but mass alone does not determine the element.
5. Conclude that the property determining the identity of an atom is the number of protons in the nucleus.