Effective capacitance of parallel combination of two capacitors C1 and C2 is 10μF . When these capacitors are individually connected to a voltage source of 1 V, the energy stored in the capacitor C2 is 4 times that of C1 . If these capacitors are connected in series, their effective capacitance will be:
a. 4.2μF
b. 3.2μF
c. 1.6μF
d. 8.4μF