(a) Account for the following: (i) Transition metals show variable oxidation states. (ii) Zn, Cd and Hg are soft metals. (iii) E^(@) value for the Mn^(3+)//Mn^(2+) couple is highly positive (+1.57 V) as compared to Cr^(3+)//Cr^(2+). (b) Write one similarity and one difference between the chemistry of lanthanoid and actinoid elements.

(a) Account for the following: (i) Transition metals show variable ox

1.	(a) Account for the following: (i) Transition metals show variable oxidation states. (ii) Zn, Cd and Hg are soft metals. (iii) E^(@) value for the Mn^(3+)//Mn^(2+) couple is highly positive (+1.57 V) as compared to Cr^(3+)//Cr^(2+). (b) Write one similarity and one difference between the chemistry of lanthanoid and actinoid elements.
Answer» Solution :(a) (i) Transition metals show variable oxidation states. This happens because of incomplete filling of d-orbitals in such a way that their oxidation states differ by unity. (ii) The d-orbitals of Zn, CD and Hg are completely filled. There is no possibility of formation of BONDS between different atoms of the elements. Hence their melting points are low. In other words, they are soft metals. (iii) `Mn^(3+)//Mn^(2+)` couple has positive `E^(@)` value because change from `Mn^(3+)` to `Mn^(2+)` involves change of configuration to half-filled d which has extra stability. `Cr^(3+)//Cr^(2+)` couple has negative Eo value because `Cr^(3+)` has stable half-filled `(t_(2g))` configuration and `Cr^(2+)` has `d^(4)` configuration which is RELATIVELY unstable and hence negative `E^(@)` value. (B) See Question Number 2 above.