Two capacitors having a capacity of 30 nf and 45 nfare connected in a string and connected to a 220 v voltage source. calculate the voltage between the condenser surfaces if they were disconnected from the voltage source and connected parallel.

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current