$A$ compound contains an $\alpha$-hydrogen atom and forms a $\beta$-hydroxy aldehyde in the presence of a dilute alkali. When this product is heated with a dilute acid,it yields unsaturated crotonaldehyde. Identify the compound.

In the reaction $CH_3CHO + HCN \to CH_3CH(OH)CN$,a chiral center is generated. The product will be ........

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

When acetaldehyde is heated with Tollen's reagent,what is obtained?

Toluene (excess) undergoes the following sequence of reactions:
$(i)$ $CrO_2Cl_2, CS_2$
(ii) $H_3O^+$
(iii) $NaHSO_3$
After filtration,a residue $(A)$ is obtained. This residue $(A)$ reacts with $dil. \ HCl$ to form compound $(B)$.
Identify the structures of residue $(A)$ and compound $(B)$ respectively.

Identify the correct statement regarding the following sequence of reactions:
$3\text{-methylbut-1-ene}$ $\xrightarrow[(ii) NaBH_4]{(i) Hg(OCOCH_3)_2/H_2O} A$ $\xrightarrow{\Delta, H_2SO_4} B (\text{major alkene})$ $\xrightarrow{O_3/Zn} C + D$