2.) Because the charges on the plates of a parrallel-plate capacitor are of opposite sign, they attract each other. Hence, it would take positive work to increase the plate separation. What happens to the external work done in this process?
Please see the attached file.
Energy stored in a capacitor is given by the relation : U = ½ CV2
Given three capacitors with capacitances C1,C2 and C3 we are required to connect them in circuit with a battery so as to store maximum energy. For the three capacitors together to store maximum energy, each capacitor must store maximum possible energy. For this, each capacitor must have maximum possible voltage across it. For this to happen, the three capacitors must be connected in parallel directly across the battery (because only then each capacitor will get the maximum possible voltage of the battery across it).
[If the capacitors are connected in ...
The questions have been answered in a logical manner highlighting the underlying principles in regards to connecting three capacitors.