CH3CHO and C6H5CH2CHO both being aliphatic aldehydes react with Tollen's reagent, Fehling solution and Benedict solution. So, these reagents cannot be used to distinguish them. CH3CHO reacts with NaOH and I2 to give yellow crystals of iodoform while C6H5CH2CHO does not react with it. CH3CHO+3I2+C6H5CH2CHO+I24NaOH⟶CHI3+HCOONa+3NaI+3H2O+NaOH⟶No reaction Thus, CH3CHO and C6H5CH2CHO can be distinguished by iodoform test.