Clemmensen reduction of ketones is carried out in

The product $(4)$ in the given reaction sequence is:

Only an aldehyde having..... can undergo the aldol condensation.

In the given set of reactions,identify $D$:
$CH_3COOH$ $\xrightarrow{SOCl_2} A$ $\xrightarrow[Anhy. AlCl_3]{Benzene} B$ $\xrightarrow{HCN} C$ $\xrightarrow{H_2O} D$

Give applications of cyanohydrins with acetaldehyde with suitable reactions. $OR$ Give following conversions by using acetaldehyde as starting material.
$(a)$ Lactic acid and acrylic acid
$(b)$ Alanine
$(c)$ $1$-amino propane-$2$-ol

Arrange these compounds in decreasing order of reactivity for the nucleophilic addition reaction :
$I.$ Acid chloride $II.$ Aldehyde
$III.$ Ketone $IV.$ Ester
Select the correct answer from the codes given below :