Find equivalent capacity `X` and `Y`
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Explanation

Let us give numbers to the four plates. Here `X` and `Y` are connected to the positive and negative terminals of the battery (say).

Here the arrangement can be represented as the grouping of three identical capacitors each of capacity `(in_(0)A)/(d)`. The arrangement will be as shown

Now the equivalent capacitance between `X` and Y` is `C_(XY)=(((C)(C))/(C+C))+C=(C)/(2)+C=(3)/(2) C`.
`C_(XY)=(3)/(2)C=(3)/(2)(in_(0)A)/(d)`.