Question

Which scientist is credited with the discovery of ‘nucleus’ in an atom?
(A) Niels Bohr
(B) Rutherford
(C) J.J. Thomson
(D) Balmer

Answer 1

Hint : The nucleus was first discovered by alpha scattering experiment. It is situated inside an atom and is extremely dense in nature and has a positive charge.

Complete step by step answer
In 1911, the nucleus of an atom was discovered. An experiment, known popularly as, the alpha scattering experiment was conducted. The scientist shot a beam of $ \alpha - {\text{particles}} $ at an extremely thin gold foil. It was observed that a major fraction of the $ \alpha - {\text{particles}} $ passed through the sheet without any deflection while some were deflected by both small and large angles(about $ {180^ \circ } $ ).
The particles are deflected due to repulsion of like charges, leading to proof that the volume that deflects the particles is positively charged. Since the particles also carry a positive charge, they are deflected.
Since most of the particles passed without any deflection, it could be concluded that most of the space in an atom is empty. This, in turn, implied that the mass of an atom was concentrated in a small portion of an atom, which must be extremely dense.
Only a few particles that are deflected by small angles imply that the positive charge in an atom is not uniformly distributed, instead it is concentrated in a small volume.
Very few of the particles that strike the nucleus of an atom, are deflected back by nearly 180 degrees. The volume of this part where the positive charge is concentrated is extremely small.
The conclusion of the experiment was that the small volume of the atom which is very dense, and positively charged is the nucleus. Most of the mass of the atom is concentrated in the nucleus. It contains the protons and neutrons.
Thus, the scientist credited with the discovery of the nucleus is Rutherford.
The correct option is Option B.

Note
James Chadwick discovered the neutrons and protons were discovered by Ernest Rutherford. J.J. Thomson discovered electrons and Niels Bohr developed Bohr's atomic model. Balmer published the formula that expressed the wavelengths of visible spectrum of the hydrogen in a simple manner.