Which property of an element is determined by adding the number of protons and the number of neutrons?

• A. Atomic mass
• B. Number of electrons
• C. Mass number
• D. Atomic number

Answer: (C)

Verified step by step guidance

1. Understand the definitions of the terms involved: The atomic number is the number of protons in an atom, which defines the element.
2. The number of electrons in a neutral atom equals the number of protons, but electrons do not contribute significantly to the mass.
3. The atomic mass is the weighted average mass of all isotopes of an element, considering their relative abundances.
4. The mass number is the sum of the number of protons and neutrons in the nucleus of an atom.
5. Therefore, the property determined by adding the number of protons and neutrons is the mass number.