Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface of the box is `8.0xx10^(3)"N-m"^(2)C^(-1)`.
What is the net charge inside the box ?

Explanation

Here, `phi=8.0xx10^(3)" N-m"^(2)C^(-1)`
If the net outward flux through the surface of the box is zero then it cannot be concluded that there is no charge inside the box. There may be equal amount of positive and negative charges inside the box. Therefore, if the net outward flux is zero, we cannot conclude that the charge inside the box is zero. One can only say that the net charge inside the box is zero.