A point charge +10 $\mathrm{\mu C}$ is a distance 5cm directly above the centre of a square of side10 cm ,as shown in the figure. What is the magnitude of the electric flux through the square?

It is given that a point charge +10 $\mathrm{\mu C}$ is located at a distance 5 cm directly above the centre of a square of side 10 cm. Let us consider  this to be a square of sides A B C D and let this be considered as one of the faces of the cube of side 10 cm. Therefore, from Gaussian theorem, the total electric flux through all six faces of the cube is given by
$\mathrm{\varphi }=\frac{\mathrm{q}}{{\mathrm{\epsilon }}_0}$
Hence, now, the flux through the square of side A B C D is obtained as
$\begin{array}{l}\mathrm{\varphi }=\frac{1}{6}\left(\frac{\mathrm{q}}{{\mathrm{\epsilon }}_0}\right)=\frac{1}{6}\left(\frac{10\times {10}^{-6}}{8.854\times {10}^{-12}}\right)\\ =1.88\times {10}^5{\mathrm{Nm}}^2/\mathrm{C}\approx 1.9\times {10}^5{\mathrm{Nm}}^2/\mathrm{C}\end{array}$