(a) Complete the following chemical equations :
(i) `MnO_(4)^(-) (aq) + S_(2)O_(3)^(2-) (aq) + H_(2)O(l) to `
(ii) ` Cr_(2)O_(7)^(2-)(aq)+Fe^(2+) (aq) + H^(+) (aq) to `
(b) Explain the following observatons :
(i) `La^(3+) (Z = 57) and Lu^(3+) (Z = 71)` do not show any colour in solutions.
(ii) Among the divalent cations in the first series of transition elements, manganese exhibits the maximum paramagnetism.
(iii) `Cu^(+)` ion is not known in aqueous solutions.

Explanation

Configurationof `La^(3+) is 4f^(0)` and that of `Lu^(3+) is 4f^(14)` . Due to the absence of partially filled f-orbitals, `La^(3+)` and `Lu^(3+)` do not show any colour in solution.