Question: why does the nucleus of an atom have a positive charge?

The nucleus of an atom is made up of protons and neutrons, the proton is positively charged while the neutron is electrically neutral. The proton got it single positive charge because of the 3 quarks it has, he quarks in the protons are the two up quarks and a single down quarks, the up quarks has a fractional charge of +2/3 each while the down quarks has a charge of -1/3, summing up the charge, the proton will have

+2/3 +2/3 -1/3 =(4-1)/3=3/3=+1 , therefore the proton has a single positive charge.