Distinction between pairs of compounds
Propanal `(CH_(3)CH_(2)CHO)` and Propanone `(CH_(3)COCH_(3))`
(a) By the use of Tollens' reagent and Fehling Solution.
(b) By iodoform test.

Explanation

Following tests help to distinguish these :
Propanal gives silver mirror with Tollen.s reagent and red ppt of `Cu_(2)O` with Fehling.s solution. Acetone (propanone) does not give this test.
(i) `underset("Propanal")(CH_(3)CH_(2)CHO)+underset("Tollens. reagent")(2[Ag(NH_(3))_(2)]^(+))+3OH^(-)`
`rarrunderset("Silver mirror")(2Agdarr+CH_(3))CH_(2)COO^(-)+4NH_(3)+2H_(2)O`
(ii) `CH_(3)CH_(2)CHO+underset("Fehling.s solution")ubrace(2Cu^(2+)+)5OH^(-)`
`rarrundersetunderset(("Red ppt."))("Cuprous oxide")(Cu_(2)Odarr+CH_(3))CH_(2)COO^(-)+3H_(2)O`
(b) Propanone is a methylketone. So, it forms iodoform (yellow ppt) with `I_(2)//NaOH`, i.e., NaOI. Propanal does not give this test.