Account for the following `:`
(i) Oxidizing power in the series `: VO^(2+) lt Cr_(2)O_(7)^(2-) lt MnO_(4)^(-)`
(ii) Actinoid contraction is greater from element to element than lanthanoid contraction.
(iii) Oxoanion of a metal show higher oxidation states.

Explanation

(i) This is due to increasing stability of the lower species to which they are reduced.
(ii) This is due to poor shielding effect of 5f electrons of actinoids than 4f electrons of lanthanoids.
(iii) This is due to high electronegativity and multiple bond formation with metal by oxygen.