if capacitors are in parallel than

potential difference across them would be same

(if a plate of capacitor is connected by wire to another capacitors plate than both will have same potential)

it is not a necessary condition for charge tobe same in both capacitor

if capacitors in series than

important condition that charge will be same on them .

and the potential difference would not be same.

for example

a capacitor c and C here connected in series bcoz potential diff. across c will be V2-V and across C V2-V1(assuming V>V2>V1)

V----------II------V2----II-----------V1

a capacitor c and C connected in parallel

  V----------------II-----------------V1

 V---------------II-----------------V1

they in parallel bcoz potential is same

but here charge may or may not be same................................................................................................

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