Complete the following chemical equation:
(i) `MnO_(4)^(-)(aq)+s_(2)O_(3)^(2-)(aq)+H_(2)O(I)`to (ii) `MnO_(4)^(-) +NO_(2)^(-)+H^(+)`to
State reason for the following :
(i) `Cu(I)` ion is not stable in an aqueous solution.
(ii) Unlike `Cr^(3+),Mn^(2+),Fe^(3+)` and the subsequently other `M^(2+)` ions of the `3d` series of elements, the `4d` and the `5d` series metals generally do not form stable cationic species.

Answer

(i) `8MnO_(4)^(-)(aq)+3S_(2)O_(3)^(2-)(g)+H_(2)O(I) to 8MnO_(2)(s)+6SO_(4)^(2-)(aq)+2OH^(-)(aq)`
(ii) `Cr_(2)O_(7)^(2-)(aq)+6Fe^(2+)(aq)+14H^(+)(aq) to 2Cr^(3+)(aq)+6Fe^(3+)(aq)+7H_(2)O(I)`.
Or
(i) `Cu^(+)` ions are not stable in aqueous solution. `Cu^(+)` in aqueous undergoes disproportationation i.e., `2Cu^(+)(aq) to Cu^(2+)(aq)+Cu(S)`.
(ii) It is because energy required energy to remove electron is more due to greater effective nuclear charge which is due to lanthanoids contraction.