$Assertion$ (A) Helium and beryllium have similar outer electronic configuration $n s^2$. $Reason$ (R) Both…
$Assertion$ (A) Helium and beryllium have similar outer electronic configuration $n s^2$.
$Reason$ (R) Both are chemically inert
Both $(A)$ and $(R)$ are correct and $(R)$ is the correct explanation of $(A)$.
Both $\mathrm{A}$ and $\mathrm{R}$ are correct but $\mathrm{R}$ is not the correct explanation of $\mathrm{A}$.
$A$ is correct but $R$ is incorrect.
Both $A$ and $R$ are incorrect.
Solution
The electronic configuration of
$\begin{aligned} \mathrm{He} & =1 s^2 \\ \mathrm{Be} & =1 s^2 2 s^2\end{aligned}$
Both have $n s^2$ configuration but helium is inert because its only shell i.e. $1 s$ is completely filled while Be is a reactive alkaline earth metal. So, A is correct but R is incorrect.