CGPET 2012 Solved Paper

Maximum oxidation states shown by a transition element =(n−1)d‌‌ unpaired electrons +ns electrons.
For 3d3,4s2,
Maximum oxidation state =3+2=5
For 3d5,4s1
Maximum oxidation state =5+1=6
For 3d5,4s2
Maximum oxidation state =5+2=7
For 3d6,4s2,
Maximum oxidation state =4+2=6
Thus, 3d5,4s2 configuration shows the highest oxidation state.