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$CH_3CHO$ and $C_6H_5CH_2CHO$ can be distinguished chemically by
A
Fehling solution test
B
Benedict test
C
Iodoform test
D
Tollen's reagent test
Detailed Solution
Both compounds are aldehydes, so both respond to Fehling's, Benedict's and Tollens' tests. These tests cannot tell them apart.
The iodoform test is given only by aldehydes and ketones that have the $CH_3-CO-$ group.
$CH_3CHO$ has this group: $CH_3CHO + 3I_2 + 4NaOH \rightarrow CHI_3 + HCOONa + 3NaI + 3H_2O$, giving a yellow precipitate of iodoform.
$C_6H_5CH_2CHO$ has no $CH_3-CO-$ group, so it gives no precipitate.
So the two are distinguished by the iodoform test.
The iodoform test is given only by aldehydes and ketones that have the $CH_3-CO-$ group.
$CH_3CHO$ has this group: $CH_3CHO + 3I_2 + 4NaOH \rightarrow CHI_3 + HCOONa + 3NaI + 3H_2O$, giving a yellow precipitate of iodoform.
$C_6H_5CH_2CHO$ has no $CH_3-CO-$ group, so it gives no precipitate.
So the two are distinguished by the iodoform test.