Which subatomic particles primarily contribute to the atomic mass of an atom?

• A. Protons and neutrons
• B. Only protons
• C. Neutrons and electrons
• D. Electrons and protons

Answer: (A)

Verified step by step guidance

1. Recall that an atom is composed of three main subatomic particles: protons, neutrons, and electrons.
2. Understand that the atomic mass of an atom is mainly determined by the mass of the particles inside the nucleus, which are protons and neutrons.
3. Note that protons and neutrons have masses close to 1 atomic mass unit (amu) each, while electrons have a much smaller mass (about 1/1836 of a proton).
4. Since electrons contribute very little to the overall mass, the atomic mass is primarily the sum of the number of protons and neutrons in the nucleus.
5. Therefore, the subatomic particles that primarily contribute to the atomic mass are protons and neutrons.