What is the capacitance of arrangement of `4` platges each of area `A` at a distance `d` in air in Fig.

Answer

`2 in_(0) A//d`

Explanation

Suppose the pair of plates `A` is connected to positive terminal of the battery and the pair of plates `B` is connected to negative terminal of the battery, Fig, As is clear from the figure, we have tow capacitors `I` and `II`. Positive plate of `I` is connected to positive plate of `II` adn negative plate to negative therefore, they are in parallel.
As `C_(p) = C_(1) + C_(2) :. C_(p) = 2C = 2 in_(0) A//d`