A transition metal x has the electronic configuration [Ar]3d${}^4$ in its +3 oxidation state. The element is:

The correct option is C Mn
Transition metal electronic configuration in $+3$ oxidation state is $\left[Ar\right]3d^4$

The neutral element electronic configuration is $\left[Ar\right]4s^{2}3d^5$, Atomic number should be $=25$. Therefore the element is $Manganese\left(Mn\right)$.