A parallel plate capacitor is charged and the charging battery is then disconnected. If the plates of the capacitor are moved further apart by means of insulating handles, then

When the battery is disconnected, the charge will remain same in any case.Capacitance of a parallel plate capacitor is given by C=ε0Ad.When d is increased, capacitance will decreases and because the charge remains the same, so according to q=CV, the voltage will increase, Hence the electrostatics energy stored in the capacitor will increase as U=12QV.