Which subatomic particle has the least mass?

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

Answer: (A)

Verified step by step guidance

1. Recall the three main subatomic particles: protons, neutrons, and electrons.
2. Understand that protons and neutrons have masses close to 1 atomic mass unit (amu), which is approximately 1.67 \times 10^{-27} kilograms.
3. Recognize that electrons have a much smaller mass compared to protons and neutrons, about 9.11 \times 10^{-31} kilograms, which is roughly 1/1836 the mass of a proton.
4. Note that an alpha particle consists of 2 protons and 2 neutrons, so its mass is roughly 4 amu, making it heavier than a single proton or neutron.
5. Conclude that among the given options, the electron has the least mass.