Which elements are considered exceptions in the classification of the periodic table?

(A) The elements $Hydrogen$ $(H)$ and $Helium$ $(He)$ are considered exceptions in the periodic table.
Position of $Hydrogen$:
$\rightarrow$ $Hydrogen$ has $1 \ e^-$ in the $1s$ orbital,suggesting it should be in group-$1$.
$\rightarrow$ $Hydrogen$ can accept $1 \ e^-$ to achieve a stable configuration like $Helium$,suggesting it should be in group-$17$.
$\rightarrow$ Due to these conflicting properties,$Hydrogen$ is placed separately in the periodic table.
Position of $Helium$:
$\rightarrow$ $Helium$ has a $1s^2$ configuration,which suggests it should be in the $s$-block.
$\rightarrow$ However,it is placed in the $p$-block with group-$18$ elements because it has a completely filled valence shell,exhibiting properties characteristic of noble gases.