Which of the following scientists discovered the electrons?

Step 1: Analyze the question The question asks which scientist discovered the electron, the negatively charged subatomic particle.

Step 2: Explain the concept Each scientist in the options is linked to a different discovery:

• Joseph John (J.J.) Thomson (1897): Used cathode ray tube experiments and found that cathode rays were streams of negatively charged particles, which were later named electrons. He also proposed the "plum pudding" model of the atom.
• James Chadwick (1932): Discovered the neutron.
• Amedeo Avogadro: Proposed Avogadro's law, which says equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. He is not linked to atomic structure.
• Ernest Rutherford (1911): Discovered the nucleus through the gold foil experiment. He is also credited with identifying the proton.

Step 3: Work through the options

• A. J.J. Thomson: discovered the electron ✔
• B. Chadwick: neutron ✘
• C. Avogadro: gas law and the mole concept ✘
• D. Rutherford: nucleus and proton ✘

Step 4: Answer The correct option is A. Joseph J. Thompson (the spelling is normally "Thomson").

Exam tip: Use this memory chain for atomic structure:

• Thomson → Tiny negative particles (electrons)
• Rutherford → Really small dense nucleus (and proton)
• Chadwick → Charge-less particle (neutron)