The photon of hard gamma radiation knocks a proton out of ${}_{12}^{24}\text{Mg}$ nucleus to form:

When a proton (${}_1^{1}p$) is removed from a nucleus:Atomic number ($Z$) decreases by $1$: $12-1=11$.Mass number ($A$) decreases by $1$: $24-1=23$.The element with atomic number $11$ is Sodium ($\text{Na}$). Thus, the resulting nuclide is ${}_{11}^{23}\text{Na}$.