Question

A proton exerts a force on a proton which is
(a) gravitational
(b) electromagnetic
(c) nuclear
(d) weak

Answer 1

(a) gravitational
(b) electromagnetic
(c) nuclear

A proton exerts gravitational, electromagnetic and nuclear forces on a proton.
The gravitational force can easily be seen everywhere; it the weakest among all the forces. It is negligible in elementary particles like protons.
The electromagnetic force can be seen between charged particles. Since proton is a charged particle, it can exert this force on other protons.
The nuclear force is present only if the interacting particles are protons or neutrons or both. So, this force can exist between two protons.