(a) (i) When propanone reacts with ethyl magnesium bromide (Grignard's reagent) and hydrolysed, it forms aldehyde.
${\left({\mathrm{CH}}_3\right)}_2\mathrm{CO}+{\mathrm{H}}_3{\mathrm{CCH}}_2\mathrm{MgBr}\underset{{\mathrm{H}}_2\mathrm{O}}{\mathit{─}\mathit{─}\mathit{─}\mathit{─}▸}$ $\underset{{\left({\mathrm{CH}}_3\right)}_2\mathrm{COH}+\mathrm{Mg}\left(\mathrm{OH}\right)\mathrm{Br}}{\underset{|}{{\mathrm{CH}}_2{\mathrm{CH}}_3}}$
(ii) When ethanal reacts with excess ethanol and acid gives acetal.

(iii) Methanal will undergo Cannizzaro reaction as it possesses $\mathrm{\alpha }$-hydrogen to form methanol.

OR
(b) (i) $\underset{\mathrm{Propanone}}{2{\mathrm{CH}}_3\mathrm{COCl}}+\underset{\mathrm{Cadmium}\mathrm{Chloride}}{{\left({\mathrm{CH}}_3\right)}_2\mathrm{Cd}}\to 2{\mathrm{CH}}_3{\mathrm{COCH}}_3$ $+{\mathrm{CdCl}}_2$
(ii)
(iii)