Where charge resides in a solid conducting sphere and a solid insulating sphere

In a charged body,there is a repulsion between like charges that create unrest.So the charges always try to minimize this repulsive force.

In case of conducting sphere,the electrons are free.So they can minimize the replusion by moving away from each other.Their separation is maximum when they are on the surface of the sphere.So in a conducting sphere,charges reside on the surface.

But in case of insulating material,the electrons are not free,they are bound to atom.So they cannot move even if they want to.So charge will reside both as surface charge and volume charge.There will be charges inside as well as on the surface.