The absolute value of potential energy (and therefore total energy ) has no physical significance. It is the difference of potential energies that matters. One can, therefore, add or subtract a constant to the potential energy (provided we do it to potential energy at every position for a given force) without any change in the physical situation. By convention, for forces which fall off to zero at large distances, the potential energy at infinity is taken to be zero. With this choice, is the potential energy positive or negaive for (a) electron bound state, (b) planet-satellite system, (c) electron-electron system?

Explanation

By convention, for forces which fall off to zero at large distances, the potential energy at infinity is taken to be zero. These forces may be attractive or repulsive. Calculations show that if the forces are attractive, then potential energy at finite distance is Negative and vice-versa. On this basis, we conclude that
(a) for electron positron bound state, Potential Energy is negative
(b) for planet satellite system, potential energy is again negative.
(c) for electron-electron system, potential energy is positive.