The correct option is D 3:2
Given:
C1=3 μF; C2=10 μF; C3=15 μF
As we know that, in a series combination, the charge on each capacitor is the same, which is the same as the charge on the equivalent capacitor.
From formula, Q=CV,
Since, here Q is constant,
∴V∝1C
⇒V2V3=C3C2=1510
So, V2V3=32
Therefore, option (d) is correct.