An electric dipole of moment $\overrightarrow{\mathrm{p}}$ placed in a uniform electric field $\overrightarrow{\mathrm{E}}$ has minimum potential energy when the angle between $\overrightarrow{\mathrm{p}}$ and $\overrightarrow{\mathrm{E}}$ is

Potential energy of a dipole in external field is given by $\mathrm{U}=-\overrightarrow{\mathrm{M}}.\overrightarrow{\mathrm{B}}$, this is maximum when the angle between the dipole and the electric field is 0^o.