Which statement about one atom of an element identifies the element?

• A. The atom has a specific mass number.
• B. The atom has a specific number of electrons in its outer shell.
• C. The atom has a specific number of protons in its nucleus.
• D. The atom has a specific number of neutrons in its nucleus.

Answer: (C)

Verified step by step guidance

1. Understand that an element is defined by the number of protons in the nucleus of its atoms. This number is called the atomic number (Z).
2. Recognize that the mass number (A) is the sum of protons and neutrons, which can vary among isotopes of the same element, so it does not uniquely identify the element.
3. Note that the number of electrons in the outer shell can change due to ionization or bonding, so it is not a definitive identifier of the element itself.
4. Understand that the number of neutrons can vary in isotopes, so it also does not uniquely identify the element.
5. Conclude that the unique and defining characteristic of an element is the number of protons in its nucleus, which determines its chemical identity.