Correct Answer - Chromium
`{:(,"Electron configuration of "M^(2+)is:,,[Ar]^(18)4s^(@)3d^(4)),( :.,"Electron configuration of"M is:,,[Ar]^(18)4s^(1)3d^(5)("and not" 5s^(2)3d^(4))):}`
So total number of electrons `= 24`.
Hence, metal `M` is chromium `(Cr)`.