Which subatomic particle is the smallest in size?

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

Answer: (D)

Verified step by step guidance

1. Understand that subatomic particles include protons, neutrons, electrons, and composite particles like alpha particles (which consist of 2 protons and 2 neutrons).
2. Recall that protons and neutrons are located in the nucleus and have roughly the same mass and size, which is significantly larger than that of electrons.
3. Recognize that an alpha particle is a cluster of 2 protons and 2 neutrons, so it is larger than individual protons or neutrons.
4. Know that electrons are fundamental particles with much smaller mass and size compared to protons and neutrons; they are often considered point particles with negligible volume.
5. Conclude that among the given options, the electron is the smallest subatomic particle in size.