Chapter 16 - Electric Potential, Energy, and Capacitance - Learning Path Questions and Exercises - Multiple Choice Questions - Page 589: 2

(a) it is reduced to one-third its original value.

The potential energy between two charges is given by $k\frac{q_{1}q_{2}}{r}$. So, potential energy is inversely proportional to distance r. So, if distance between the charges is tripled, then the potential energy reduces to one-third its original value.