Which subatomic particle is the least massive?

• A. Electron
• B. Proton
• C. Neutron
• D. Alpha particle

Answer: (A)

Verified step by step guidance

1. Recall that subatomic particles include electrons, protons, and neutrons, each with different masses.
2. Understand that an alpha particle is not a single subatomic particle but a combination of 2 protons and 2 neutrons, so it is heavier than individual subatomic particles.
3. Compare the masses of the three fundamental subatomic particles: electrons, protons, and neutrons. Protons and neutrons have masses close to 1 atomic mass unit (amu), while electrons have a much smaller mass.
4. Recognize that the electron's mass is approximately 1/1836 that of a proton, making it the least massive among the options.
5. Conclude that the electron is the least massive subatomic particle compared to protons, neutrons, and alpha particles.