Consider a closed surface of arbitatry shape as shown in figure. Suppose a single charge `Q_1` is located at some point within the surface and second charge `Q_2` is located outside the surface.

a. What is the total flux passing through the surface due to charge `Q_1`?
b. What is the total flux passing through the surface due to charge `Q_2`?

Explanation

a. Since `Q_1` is inside the surface, so flux due to `Q_1` is
`Q_1//epsilon_0`.
b. Since `Q_2` is outside, so there is no contribution to
the flux due to `Q_2`.