A charge Q is placed at a distance a/2 above the centre of the square surface of edge a as shown in the figure. The electric flux through the square surface is:

A

$$\frac{Q}{3\varepsilon_0}$$

B

$$\frac{Q}{6\varepsilon_0}$$

C

$$\frac{Q}{2\varepsilon_0}$$

D

$$\frac{Q}{\varepsilon_0}$$