Which of the following is an example of the strong nuclear force acting in an atom?
a. a proton repelling a proton
b. a neutron attracting a neutron
c. a neutron repelling an electron
d. an electron attracting a proton

B.A neutron attracting a neutron

Explanation:

Nuclear force is a fundamental force which act at small distance range. Its range of distance work for fermi order distances which means for the range of radius of nuclei this force will work.

It is the strongest force among all fundamental forces and only depends on the distance between two nuclei. If distance range is more than fermi order range then the nuclear force will be zero.

So this force neither depends on mass nor it depends on charge of two particles. It will change its magnitude of attraction or repulsion as we change the distance between two particles.

For a very short range of distance nuclear force is always repulsive force while for other comparative larger distance range it is always attractive.

So here correct answer would be

B.A neutron attracting a neutron