You can't say for sure with that little information.
I assume that the original question had a little more context to it, because you can't give a definitive answer with this little information.
Take a look at the electron configuration template given to you
#["Ar"] 4s^x 3d^y#
What do you know for sure? Well, you know that you're dealing with an element that's located in the fourth period of the periodic table, since the noble gas shorthand notation given uses argon,
That is the case because you're missing a p-subshell, which means that elements from gallium,
#["Ar"] 4s^2 3d^10 4p^1 " "#to #" "["Ar"] 4s^2 3d^10 4p^6#
The same can be said for the first two elements of the period, potassium,
#["Ar"] 4s^1 " "#and #" "["Ar"] 4s^2#, respectively.
In other words, the first wo elements of the period do not have their d-subshell occupied with electrons.
So that leaves you with a transition metal as the possible candidate.
You can get the electron configurations for the group four transition metals here
My guess is that you are dealing with one of the two elements that have an "anomalous" electron configuration, cromium or copper.
Their electron configurations are
#["Ar"] 3d^5 4s^1 " "#and #" "["Ar"] 3d^10 4s^1#, repspectively.
Again, without proper context, you can't say for sure which transition metal you have.