An element has electronic configuration [Ar] 3d4 in its +3 oxidation state.What will be the electronic configuration of its atom?

We are given that the electronic configuration of the element in +3 oxidation state is [Ar]3d⁴. Thus, the atomic number of the element should be 

= atomic number of argon + 4 +3

= 18 + 4 + 3

= 25

Thus, the element is manganese and its electronic configuration is [Ar]4s²3d⁵.