The largest oxidation number exhibited by an element depends on its outer electronic configuration. With which of the following outer electronic configurations the element will exhibit largest oxidation number?

Highest oxidation number of any transition element = (n - 1) d-electrons + ns-electrons. Therefore, larger the number of unpaired electrons in the 3d-orbitals, higher is the oxidation number. (a) 3d14s2=3  (b) 3d34s2=3+2=5   (c) 3d54s1=5+1=6 and  (d) 3d54s2=5+2=7