What must be the charge on each of two 100 kg spherical masses in order for the electrical force to be equal to the gravitational force?

The electrical force between the two masses is equal to the gravitational force when the magnitude of the electrical force, given by Coulomb's law, is equal to the magnitude of the gravitational force, given by Newton's law of universal gravitation. By setting these equal and solving for charge, you can find that the charges on the two masses must be around 1.45 x 10^17 C each.