Consider the reactions :
`2S_(2)O_(3(aq))^(2-)+I_(2(s))toS_(4)O_(6(aq))^(2-)+2I_((aq))^(-)`
`2S_(2)O_(3(aq))^(2-)+2Br_(2(l))+5H_(2)O_((l))to2SO_(4(aq))^(2-)+4Br_((aq))^(-)+10H_((aq))^(+)`

Explanation

In `S_(2)O_(3)^(-2)`, oxidation number of S is +2. Where in `S_(4)O_(6)^(-2)` is +2.5. In `SO_(4)^(-2)`, oxidation number of S is +6.
`Br_(2)` is strong oxidising agent than `I_(2)`. So `Br_(2)` is convert `S_(2)O_(3)^(-2)` into `SO_(4)^(-2)`. In which oxidation number of oxygen is `S_(2)O_(3)^(-2)` is (+2) and `SO_(4)^(-2)` is (+6). So, it is oxidise (+2) into (+6).
While `I_(2)` is weak oxidizing agent. Therefore, it oxidised `SO_(3)^(-2)` (S = +2) to `S_(4)O_(6)^(-2)` (S = +2.5). Therefore, it gives different reactions.