Answer
$H_{(g)}$.
Work Step by Step
$Na_{(s)}$, $Ne_{(g)}$, $CH_{4(g)}$,
$S_{8(s)}$ and $Hg_{(l)}$ are in their standard states. These elements are stable at $25^{\circ}C$ and 1 bar pressure and occur in pure form. In the standard state standard enthalpy of formation is zero.
$H_{(g)}$ is not the stable standard state at $25^{\circ}C$ and 1 bar pressure. Therefore the standard state standard enthalpy of formation of $H_{(g)}$ is not equal to zero.
The stable standard state of hydrogen is $H_{2(g)}$