Discovery of the nucleus of an atom was due to the experiment carried out by:

A.Bohr
B.Rutherford
C.Moseley
D.Thomson

Hint:
 Nucleus is the center part of an atom that is made up of protons and neutrons. It has an overall positive charge on it. It is the place where the majority of the atom's mass is present.

Complete step-by-step answer:

Bohr: An atom consists of a central positive part called the nucleus which contains all the protons and neutrons. Electrons which are present outside the nucleus revolve around the nucleus in definite circular paths called orbits or shells. Each orbit can accommodate not more than a fixed number of electrons.
Rutherford: According to Rutherford, all protons are present inside the nucleus, which is situated at the center of the atom. Electrons reside outside the nucleus and revolve around the nucleus in well-defined orbits.
Moseley: He proposed that the atomic number can be used as the organizing principle instead of atomic mass. According to Moseley's Periodic Law, the properties of elements are a periodic function of their atomic numbers. If the elements are arranged in order of their increasing atomic number then elements with similar properties are repeated after a regular interval.
Thomson: An atom consists of a sphere(or ball)of positive charge with negatively charged electrons embedded in it. The positive and negative charges in an atom are equal in magnitude, due to which an atom is electrically neutral. It has no overall positive or negative charge.
As we can see that Rutherford discovered the nucleus.
The correct option is B.

Note:
The possibility to make a mistake is that you may choose option A.
The Rutherford model came before the Bohr model, so he discovered the nucleus after Bohr's model built upon it.