Explain the variation in the oxidation states of 3d-block elements. 

Explanation

(i) From Sc to Mn, the minimum oxidation state is the number of electrons present in 4s-orbital and maximum oxidation state is the sum of the electrons present in 4s- and 3d-orbitals. Example: `Mn (3d^54s^2) : +2, +3, +4, +5, + 6, +7.`
  (ii) From Fe to Zn, the maximum oxidation state decreases from + 6 to + 2. It is due to the pairing of electrons in the 3d - subshell and removal of these electrons becomes difficult. Example: `Zn (3d^(10) 4s^(2))`.