Which one of the elements with the following outer orbital configurations may exhibit the largest number of oxidation states? [CBSE AIPMT 2009]

The correct option is C

$3d^5,4s^2$

The sum of number of electrons (unpaired) in d-orbitals and number of electrons in s-orbital gives the number of oxidation states (os) exhibited by a d-block element. Therefore,
(a) $3d^3,4s^2\Rightarrow OS=3+2=5$
(b) $3d^5,4s^1\Rightarrow OS=5+1=6$
(c) $3d^5,4s^2\Rightarrow OS=5+2=7$
(d) $3d^2,4s^2\Rightarrow OS=2+2=4$
Hence, element with $3d^5,4s^2$ configuration exhibits largest number of oxidation states.