Which of the following best describes the difference between atomic mass and atomic number?

• A. Atomic mass is the number of protons, while atomic number is the total number of protons and neutrons.
• B. Atomic mass is always equal to the atomic number for all elements.
• C. Atomic mass is the total number of protons and neutrons in an atom, while atomic number is the number of protons.
• D. Atomic mass is the number of electrons in an atom, while atomic number is the number of neutrons.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the definition of atomic number. The atomic number is the number of protons in the nucleus of an atom. It uniquely identifies an element.
2. Step 2: Understand the definition of atomic mass. Atomic mass (or mass number) is the total number of protons and neutrons in the nucleus of an atom.
3. Step 3: Recognize that electrons have negligible mass compared to protons and neutrons, so they do not significantly affect atomic mass.
4. Step 4: Compare the two definitions: atomic number counts only protons, while atomic mass counts both protons and neutrons.
5. Step 5: Conclude that the correct description is: atomic mass is the total number of protons and neutrons in an atom, while atomic number is the number of protons.