Identify an aldehyde used in margarine and in food for its buttery odour.

The reaction of $A$ to give $B$ and $C$ as shown in the reaction scheme is an example of:
$CH_2=CH_2$ $\xrightarrow[2. Zn/H_2O]{1. O_3} A$ $\xrightarrow{Conc. NaOH} B + C$
(Where $B$ is an alcohol and $C$ is a sodium salt of a carboxylic acid)

Ketones react with $Mg-Hg$ followed by treatment with water to give:

$\alpha-H$ containing aldehyde and ketone reacts with dil $NaOH$ and gives $\beta-hydroxy$ aldehyde or $\beta-hydroxy$ ketone. This reaction is called $-$

Which one of the following reacts with $HCN$ and Tollen's reagent,but is not oxidised by Fehling's solution?

$CH_3-C(O)-CH_2-CH_2-CH_2-CH_2-CHO \xrightarrow{HO^{-} / \Delta} (A) (73\%)$
Product $(A)$ is