At 10–10 s during the evolution of the universe, formed, which are elementary particles that make up protons and neutrons.

Proton is the fundamental particle  that is found in every elements.Similarly neutron is also present in every atoms except normal hydrogen atom though it is present  in other isotopes of hydrogen also

The proton and neutron are included in the hadron family which are composed of  quark particles .

There are various types of quark particles with their anti particles also. These are named as UP, DOWN, TOP,BOTTOM,CHARM and STRANGE with their anti particles like ANTI-UP,DOWN etc.

These are held by strong forces just like electromagnetic force and becomes the building block of protons and neutrons.

One proton is made up of two up quarks and one down quark. The charge of one up quark is and charge of one down quark is

Hence charge of proton is e

                                         = +e

One neutron is made up of one up quark and two down quarks.

Hence charge of neutron is- e

                                           =0

explanation:

the masses of the objects and the distance between them

they should be similar or the same