The majority of an atom's mass comes from which two subatomic particles?

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

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 protons and neutrons are located in the nucleus of the atom, while electrons orbit around the nucleus.
3. Recognize that protons and neutrons have masses approximately 1 atomic mass unit (amu) each, whereas electrons have a much smaller mass (about 1/1836 of a proton).
4. Since the mass of electrons is negligible compared to protons and neutrons, the majority of an atom's mass comes from the particles in the nucleus.
5. Therefore, the two subatomic particles that contribute most to the atom's mass are protons and neutrons.