How can we distinguish chemically the following pairs of compounds?
(i) `CH_(3)CHO` and `CH_(3)COCH_(3)`
(ii) `CH_(3)CHO` and `C_(6)H_(5)CHO`
(iii) `C_(6)H_(5)COCH_(3)` and `C_(6)CH_(5)COC_(6)H_(5)`
(iv) `CH_(3)CHO` and `CH_(3)CH_(2)CHO`

Explanation

(i) `CH_(3)CHO` gives +ve Tollens test and forms silver mirror with ammoniacal `AgNO_(3)`
`CH_(3)CHO +[Ag(NH_(3))_(2)]^(+) to CH_(3)COO^(-) +Ag darr`
While `CH_(3)COOH_(3)` does not give this test.
(ii) `CH_(3)CHO` forms silver mirror with Tollen's reagent while does not give this test.
(iii) gives +ve iodoform reaction and forms a yellow ppt of `CH_(3)I` as it as a methyl ketone while
does not give this reaction.
(iv) `CH_(3)CHO` shows idoform reaction whereas `CH_(3)CH_(2)CHO` does not.