Key Idea Number of oxidation states exhibited by d-block elements is the sum of number of electrons (unpaired) in d-orbitals and number of electrons in s-orbital. (a) 3 d3,4 s2⇒O.S=3+2=5 (b) 3 d5,4 s1⇒O.S=5+1=6 (c) 3 d5,4 s2⇒O.S=5+2=7 (d) 3 d2,4 s2⇒O.S=2+2=4 Hence, element with 3 d5,4 s2 configuration exhibits largest number of oxidation states.