Cr2O27−+SO23−⟶Cr+3+SO24−In the above reaction, in Cr2O27−,Cr is in +6 oxidation state which get convert to +3 oxidation state.
As there are two atoms of Cr, so total e− transfer will be 2∗3=6
In SO23−,S is in +4 oxidation state
In SO24−,S is in +6 oxidation state
Therefore; total number of e− transfer is 2.