Q. Which of the following pair/s is/are correctly matched?
1.J.J. Thomson       :       Discovery of electron
2.E. Rutherford       :       Discovery of the atomic nucleus
3.J. Chadwick       :       Discovered of neutrons
Choose the correct answer from below given codes:

[A] 1 only

[B] 1 and 2 only

[C] 2 and 3 only

[D] 1, 2 and 3

Answer: D
Notes:

Explanation: Credit for the discovery of electron and proton goes to J.J. Thomson and E.Goldstein, respectively. J.J. Thomson proposed that electrons are embedded in a positive sphere.

  • Rutherford’s alpha-particle scattering experiment led to the discovery of the atomic nucleus. Rutherford’s model of the atom proposed that a very tiny nucleus is present inside the atom and electrons revolve around this nucleus. The stability of the atom could not be explained by this model.
  • Neils Bohr’s model of the atom was more successful. He proposed that electrons are distributed in different shells with discrete energy around the nucleus. If the atomic shells are complete, then the atom will be stable and less reactive.
  • Chadwick discovered presence of neutrons in the nucleus of an atom. So, the three sub-atomic particles of an atom are: (i) electrons, (ii) protons and (iii) neutrons. Electrons are negatively charged; protons are positively charged and neutrons have no charges.

Source: Science NCERT