Question

What is the electric flux passing through a Gaussian surface that contains 2 protons and 1 electron?

Answer 1

The Gauss's law says

$$\phi=\oint {\bf E}d{\bf A}=\frac{q_{\rm net}}{\epsilon_0}$$

Hence, the electric flux passing through a Gaussian surface that contains 2 protons and 1 electron

$$\phi=\frac{2e-e}{\epsilon_0}=\frac{e}{\epsilon_0}\\ =\frac{1.6*10^{-19 }}{8.85*10^{-12}}=1.8*10^{-8}\:\rm N\cdot m^2/C$$