The force exerted by a neutron on a proton is

Both the neutron and the proton have mass, so they exert a gravitational force on each other.

They are both nucleons, so they interact via the strong nuclear force.

Both particles are composed of quarks and participate in weak interactions, so they exert a weak force on each other.

Although the neutron has zero net electric charge, it is composed of charged quarks and possesses a non-zero magnetic dipole moment. Therefore, it exerts an electromagnetic force on the proton.

Thus, all four types of forces are exerted by a neutron on a proton.