Which of the following determines the identity of an atom?

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

Answer: (B)

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 the nucleus.
2. Recall that the total mass of the atom is determined by the sum of protons and neutrons, but this does not define the element itself.
3. Recognize that the number of neutrons can vary in atoms of the same element, resulting in different isotopes, but the element remains the same.
4. Note that the number of electrons can change when atoms become ions, but this does not change the element's identity.
5. Conclude that the key factor determining the identity of an atom is the number of protons in its nucleus.