In the simplified model of the atom, what determines the identity of an atom (i.e., what element it is)?

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

Answer: (D)

Verified step by step guidance

1. Understand that the identity of an atom, meaning which element it is, is determined by a fundamental property of its nucleus.
2. Recall that the nucleus of an atom contains protons and neutrons, but only one of these determines the element's identity.
3. Recognize that the number of protons in the nucleus is called the atomic number, often represented as \(Z\).
4. Know that changing the number of protons changes the element itself, while changing neutrons creates isotopes of the same element.
5. Therefore, the key factor that determines the identity of an atom is the number of protons in its nucleus, or the atomic number.