A point charge $+20 \mu C$ is at a distance $6 cm$ directly above the centre of a square of side $12 cm$ as shown is figure. The magnitude of electric flux through the square is

From figure, it is clear that square $ABCD$ is one of the six faces of a cube of side $12 cm$. By Gauss's theorem, total electric flux through all the six faces of the cube $=\frac{q}{{\epsilon }_0}$

$\therefore$ Electric flux through the square

$\varphi = \frac{1}{6}\frac{q}{{\epsilon }_0}= \frac{1}{6}\times \frac{20\times {10}^{-6}}{8.85\times {10}^{-12}} = 3.8\times {10}^5 N m^2 C^{-1}$