An electric dipole consisting of charges + q and – q separated by a distance L is in stable equilibrium in a uniform electric field $\overrightarrow{\mathrm{E}}$. The electrostatic potential energy of the dipole is

We know electrostatic potential energy of the dipole is given by : 
$\mathrm{P}=-\mathrm{pE} ...\left(1\right)$
Here , p is electric dipole defined by product of charge and distance between them .
p = qL .
Putting value of p in equation 1,
We get , P=-qLE
(C) -qLE