Balance the following redox reactions by ion -electron method:
`Cr_(2)O_(7)^(2-) +SO_(2)(g)toCr^(3+)(aq)+SO_(4)^(2-)(aq)` (in acidic solution)

Explanation

Oxidation reaction : `SO_(2)(g)+2H_(2)OtoSO_(4)^(2-)(aq)+4H^(+)(aq)+2e`
Reduction reaction :
`Cr_(2)O_(7)^(2-)(aq)+14H^(+)(aq)+6eto2Cr^(3+)+(aq)2Cr^(3+)(aq)+7H_(2)O(l)`
Multipying equation (1) and (2) then adding it to equation (2), we have
`CrO_(7)^(2-)(aq)+3SO_(2)(g)+2H^(+)(aq)to3Cr^(3+)(aq)+3SO_(4)^(2-)+H_(2)O(l)`