Which of the following reactions is used to detect the presence of a carbonyl group?

$A$ mixture of benzaldehyde and formaldehyde on heating with aqueous $NaOH$ solution gives :-

Which one of the following is used for the purification of aldehydes?

Assertion: Acetoacetic ester,$CH_3COCH_2COOC_2H_5$,will give iodoform test.
Reason: It does not contain $CH_3CO-$ group.

Given below are two statements $:$
Statement $(I) :$ Vanillin,with the structure shown below,will react with $NaOH$ and also with Tollen's reagent.
Statement $(II) :$ Vanillin will undergo self-aldol condensation very easily.
In the light of the above statements,choose the most appropriate answer from the options given below $:$

The reagent that can distinguish benzaldehyde from propionaldehyde is