Question

The existence of nucleus was discovered by
(i) Bohr
(ii) J. J. Thompson
(iii) Goldstein
(iv) Rutherford

Answer 1

Try to think what contributions each scientist made to the discovery of the atomic model that is being studied today. Then eliminate the ones whose discovery was not related to the existence of the nucleus. Identify the one who made the correct approach to the discovery of the nucleus.

Complete step by step answer:
- J. J. Thompson suggested an atomic model which model considered the electrons as embedded in a sphere of uniform positive charge. This model was unsatisfactory for many reasons including its inability to explain atomic spectra and was ultimately discarded.
- The first correct approach of atomic structure was made only when it was established that atoms possess nucleus. The corresponding atom model was discovered by Rutherford and is called the nuclear model of the atom.
- Rutherford's atomic model had limitations including the fact that the atom was not stable. This discrepancy was solved by Bohr who applied quantum theory of radiation to interpret the results.
- Goldstein discovered the canal rays.
So the existence of nucleus was first discovered by Rutherford.

Hence the correct answer is (iv) Rutherford.

Additional Information:
- Rutherford performed the Gold Foil experiment where he bombarded a thin gold foil with alpha particles and detected their deflection. During the experiment most of the alpha particles passed without any appreciable deviation.
- Few of them underwent minor deviations while $1$ in $20000$ deviated by large angles and retraced their path. According to Rutherford wide angle scattering cannot occur by any additive effect of a number of small collisions but was due to a single collision.
- From the angle of scattering he made an idea of the charge of the target that scattered the alpha particles. He concluded that the entire mass and positive charge of the atom is concentrated in a central position which was termed as the nucleus of the atom.

Note: A positively charged nucleus is composed of an atom, with a cloud of negatively charged electrons surrounding it together bound by electrostatic force.