Which property of an atom determines the identity of an element?

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

Answer: (D)

Verified step by step guidance

1. Understand that the identity of an element is defined by a fundamental property of its atoms.
2. Recall that atoms consist of protons, neutrons, and electrons, each with different roles.
3. Recognize that the number of protons in the nucleus, called the atomic number, uniquely identifies an element.
4. Note that while electrons can vary in number (forming ions) and neutrons can vary (forming isotopes), these do not change the element's identity.
5. Therefore, the property that determines the identity of an element is the number of protons in its nucleus.