Every system has a tendency to lower it's energy.  For a system of 2 like/unlike charges (q1,q2), the energy of the system is given by the equation U=k(q1)(q2)/r where U=potential energy k=constant for a medium(medium is one in which charges are kept eg air, water etc.) q1,q2=charges(including their sign, positive or negetive) r=dist. between charges For U to be minimum, r should be maximum, everything else kept constant. therefore, like charges move away to increase r.  Incase of unlike charges one will be negetive and other positive. Let q1 be negetive, so U=k(-q1)(q2)/r Now, for U to be minimum, r should be minimum so charges attract. Hence like charges repel and unlike attract.
						

							
hi
in case of a charge say a +ve and a -ve, force acting on +ve charge is -1/4(pie*epsilon not)*q1*q2/r2. thus the force acting is
nothing but force of attraction .thus unlike charges attract and vice versa.
						

							
force = qE
E = electric field
now , we have two cases....distance bw A & B is d ...
 A                         B
-q                        -q                          case1
+q                       +q                          case2
for case 1 , electric field due to A at B is towards BA , force on charge B
will be towards AB ...
that means charges will move away from each other or we can say that
repulsive force exists bw them ...
 
for case2 , electric field due to A at B is towards AB , force on B will be towards AB
so they will againg repel...
						

							this is a very tough question and no one other than a great physicst will be able to answer it satisfactorily..however if u have some knowledge of quarks then u can have some idea about it. It depends on the movement of quarks, rotation and revolution inside protons or electrons which is responsile for their type of +ve or-ve charge. Study particle physics n quantum mechanics if u want to know more.
						

							
Due to their nature
f positive and negative charges
and the quantisation which is ne +-