Assertion: According to Gauss' law, $\oint \overrightarrow{E}.d\overrightarrow{A}=\frac{\mathrm{\Sigma }q}{{\epsilon }_0}$. Here, $\overrightarrow{E}$ is the resultant electric field due to all charges present inside as well as outside the closed surface. On the other hand, the charge $q$, appearing in the law, is only the charge contained within the closed surface.

Reason: Gauss' law is applicable for fields which are conservative and obey inverse square law.