(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 Mn³⁺/Mn²⁺ couple is highly positive (+ 1·57 V) as compared to Cr³⁺/Cr²⁺ . 56/1 12
(b) Write one similarity and one difference between the chemistry of lanthanoid and actinoid elements.

(a) (i) ns-electrons, (n-1) d electron has similar energy. They both can be removed easily. Therefore, transition elements show variable oxidation state.
(ii) These elements have completely filled d orbital due to which they form weak metal-metal bonds. Therefore, Zn, Cd, and Hg are soft metals.
(iii) When Mn³+ is converted to Mn²⁺ it attains the stable half-filled d5 configuration. Which results in large E0 value. While Cr³⁺ (d³) when converted into Cr ²⁺(d²) it goes to less stable configuration.
(b) The atomic radius of both lanthanoids and actinoids decreases with increase in atomic number.
All the Lanthanoids are non-radioactive except promethium while all the actinoids are radioactive.