Two conducting plates P and Q with large surface area A are placed as shown in figure. A charge q is given to plate P. The electric field between the plate at any point is

$\frac{q}{2 A \varepsilon_0}$

Charge distribution will be as shown 

Field at point B

$=\frac{q-q'}{2 A \varepsilon_0}-\frac{q'}{2 A \varepsilon_0}+\frac{q'}{2 A \varepsilon_0}-\frac{q'}{2 A \varepsilon_0}=\frac{q}{2 A \varepsilon_0}$

∴ (B)