Correct Answer - C
Once CHO is oxidised to `COO^(-)` and one CHO is reduced to `CH_(2)OH`.
Thus, it is a disproportionation reaction. Thus, (a) and (b) is true and `overset(CHO)overset(|)(CHO)` is reducing as well as oxidising agent.
Thus, (d) is also true, Thus , ( c) is incorrect.