Final answer:
When the two conducting spheres touch, the total charge of the two spheres spreads out across the whole surface of the spheres. When they are moved apart again, each sphere is left with half of the total original charge, resulting in a charge of -4 nC on each sphere.
Step-by-step explanation:
When the two conducting spheres are brought together to touch, they become one single big conductor and the total charge of the two spheres spreads out across the whole surface of the touching spheres. When the spheres are moved apart again, each one is left with half of the total original charge.
Before the spheres touch, the total charge is -5 nC + (-3) nC = -8 nC. When they touch, they share out the -8 nC across their whole surface. When they are removed from each other, each is left with half of the original charge, which is -4 nC.