Electric Charge and Electric Field: Study Notes

The image above shows two conducting spheres inside two separate insulated boxes. Initially, the left box contains one sphere with a charge of $+2\ \mathrm{C}$ and another with $-1\ \mathrm{C}$. The right box contains one sphere with $+3\ \mathrm{C}$ and another with $-2\ \mathrm{C}$. If the spheres in each box are brought into contact and then separated, what will be the final charge on each sphere in the left box?

After the spheres in the right box (with initial charges $+3\ \mathrm{C}$ and $-2\ \mathrm{C}$) are brought into contact and then separated, what is the final charge on each sphere?

Which principle is illustrated by the process of bringing the spheres into contact and then separating them, as shown in the image?