Which subatomic particle was discovered first?

• A. Electron
• B. Neutron
• C. Positron
• D. Proton

Answer: (A)

Verified step by step guidance

1. Understand the historical timeline of subatomic particle discoveries to determine which particle was identified first.
2. Recall that the electron was discovered by J.J. Thomson in 1897 through cathode ray tube experiments, marking the first identification of a subatomic particle.
3. Note that the proton was discovered later by Ernest Rutherford in 1917 through nuclear reaction experiments.
4. Recognize that the neutron was discovered by James Chadwick in 1932 by observing nuclear reactions involving beryllium and alpha particles.
5. Understand that the positron, the electron's antiparticle, was discovered by Carl Anderson in 1932 through cosmic ray experiments.