Question

The scientist who is credited with the discovery of ‘nucleus’ in an atom is:
A. Niels Bohr
B. Rutherford
C. J.J. Thomson
D. Balmer

Answer 1

Hint: Atoms are electrically neutral, the positive charge on the nucleus is equal to the total negative charge of all the orbiting electrons. Atoms mostly consist of space. Atoms consist of three particles: proton electron and neutron. Protons and neutrons together constitute a nucleus. Geiger and Marsden did experiments and found that some of the alpha particles are deviated rather than going straight. This led to the famous gold foil experiment, which led to discovery of nucleus.

Complete step by step answer:
The concept of nucleus in an atom is the most important contribution of scientist Rutherford and his model is a landmark in the development of the modern atomic theory.
An experiment was performed by Geiger and Madsen. In this experiment, a narrow beam of alpha particles from a radioactive source was incident on the gold file. The scattered alpha particles were detected by a detector fixed at a rotating stand. The whole setup is evacuated in the chamber. They observed the number of alpha particles as a function of scattering angle. The deviation of alpha particles from its original direction is the scattering angle.
It is observed that most of the alpha particles passed undeviated and only few are scattering. This anomalous behaviour seems interesting to Rutherford and on the basis of observations made by Geiger and Marsden, he proposed his own atomic model. He said that a large scattering angle is possible only because alpha particles are repelled by a massive positive charge in a very small space. He called this massive centre a nucleus.
By studying scattering of alpha particles and the trajectory of the scattered alpha particle, he determined the size of the nucleus which is ten raised to the power minus 15 to ten raised to the power minus 14 meter. Size of the nucleus is found 100000 times smaller than the size of an atom. According to Rutherford, the atom has a tiny positively charged core called nucleus. The total charge and mass is included in the nucleus only. Nucleus is surrounded by negatively charged electrons orbiting around the nucleus in circular orbits.

Hence option (B) is correct

Note: Upto 1897, it was believed that atoms were invisible until J.J. Thomson discovered electrons. He showed that electrons have a negative charge on it. After that Rutherford came with nucleus theory. He showed that an atom has a massive portion inside it known as a nucleus. Rutherford theory was unable to explain the hydrogen spectrum. One of the series of hydrogen spectrum was explained by Balmer. Neild Bohr, in 1913 modified the theory of Rutherford.