Which of the following subatomic particles is the smallest in mass?

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

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the question is asking to compare the masses of different subatomic particles: proton, electron, alpha particle, and neutron.
2. Step 2: Recall the approximate masses of each particle: proton and neutron have masses close to 1 atomic mass unit (amu), electron has a much smaller mass (about 1/1836 of a proton), and an alpha particle consists of 2 protons and 2 neutrons, so its mass is roughly 4 amu.
3. Step 3: Compare these masses directly: electron mass << proton mass ≈ neutron mass < alpha particle mass.
4. Step 4: Conclude that the electron is the smallest in mass among the given options.
5. Step 5: Understand that this difference in mass is fundamental to atomic structure and behavior, with electrons being much lighter and responsible for chemical properties, while protons and neutrons form the nucleus.