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

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Solution

(a)(i) Transition metals exhibit variable oxidation states due to different energy requirements.
(ii) Because they do not exhibit covalency as their (n-1)d orbital is fully filled, So they are soft.
(iii) Because Mn is more reactive than Cr.
(b) Difference:
$\begin{matrix} Lanthanoid & Actinoid - Less tendency of complex formation. & - High tendency of complex formation. - do not form oxo cations. & -Form oxo cation. \end{matrix}$

Similarity : In both cases f- orbitals are progressively filled.

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