Two identical capacitors connected in parallel are charged to a potential V. They are then separated and connected in series.What will happen to the energy, potential difference and charge of the combination?

initially,both the capacitors will have charge cv and potential drop across each capacitor is v.

now when they are connected in series to a potential difference v,the potential drop across each capacitor is v/2. Thus,the charge stored by each capacitor reduces to cv/2.The energy stored reduces by 4 times.