Two equal point charges each of charge 'q' are placed at a distance of 2a from each other and a third charge -2q in placed at the mid point between them. The potential energy of the system is:

$\frac{q}{8 \pi \varepsilon_0 a}$ $\frac{6 q^2}{8 \pi \varepsilon_0 q}$ $\frac{-7 q^2}{8 \pi \varepsilon_0 a}$ $\frac{-9 q^2}{8 \pi \varepsilon_0 a}$

$\frac{-7 q^2}{8 \pi \varepsilon_0 a}$

The correct answer is Option (3) → $\frac{-7 q^2}{8 \pi \varepsilon_0 a}$