In which of the following there is a change in oxidation number ?
(a) An aqueous solution of `CrO_(4)^(2-)` is acidified.
(b) `SO_(2)` gas is passed through acidified `Cr_(2)O_(7)^(2-)` solution.
(c) `Cr_(2)O_(7)^(2-)` solution is made alkaline.
(d)` CrO_(2)Cl_(2)` is dissolved in NaOH.

Explanation

(a) `overset(+6)(2[CrO_(4)]^(2-))+2H^(+) to overset(+6)([Cr_(2)O_(7)]^(2-))+H_(2)O` : no change in O.N
(b) `overset(+6)([Cr_(2)O_(7)]^(2-))+overset(+4)(3SO_(2))+2H^(+) to overset(+3)(2[Cr]^(3+))+overset(+6)(3[SO_(4)]^(2-))+H_(2)O` :Change in O.N
(c) `overset(+6)([Cr_(2)O_(7)]^(2-))+2OH^(-) tooverset(+6)(2[CrO_(4)]^(2-))+H_(2)O` :No Change in O.N.
(d) `overset(+6)(CrO_(2))Cl_(2)+2NaOH to Na_(2) overset(+6)(CrO_(4))` :No change in O.N