Two capacitors having capacitances C₁ and C₂ are charged with 120 V and 200 V batteries, respectively. When they are connected in parallel now, it is found that the potential on each one of them is zero. Then, 

Given V₁ = 120 V and V₂ = 200 V 

When total charge of the capacitors is zero , the common potential will be equal to zero.

Here given that potential is zero for each capacitor, then their charge must same, i.e. C₁V₁=C₂V₂

           120 C₁ = 200 C₂

              12 C₁ = 20C₂

$\Rightarrow$            3C₁ = 5C₂