We know from Gauss Law that the closed surface integral of electric flux density () is equal to the charge enclosed () by that closed surface. This is mathematically given by

The electric flux is given by

Let us consider a point charge +q with electric field lines going away from it. We will consider following two scenarios

Scenario 1: Gaussian surface S is chosen around +q charge as shown below

From the Gauss’s law, the expression (2) will be

Also, we can see that the flux lines are going outward from the surface.

Scenario 2: Gaussian surface S is chosen as shown in the figure below

We can see that there is no charge inside the chosen surface S and all the charge is outside of this surface. Also, same number of electric flux lines entering this surface emerges out from this surface. Therefore, by Gauss’s law, the expression (2) will be

However, is not zero.

Therefore, option C and D are correct.