Answer : (c) $\;2.2\times10^{-12}\;C$
Explanation : Electric flux through five surfaces is zero . The electric flux through on surface x=a plane is :
$\phi=\large\frac{\in_{0}\;a}{l}\;a^2=\large\frac{Q}{\in_{0}}$
$Q=\large\frac{\in_{0}\;a^3\;\in_{0}}{l}$
$Q=\large\frac{5\times10^3\times10^{-6}\times8.86\times10^{-12}}{2\times10^{-2}}$
$Q=2.2\times10^{-12}\;.$