Which one of the following compound undergoes disproportionation in the presence of concentrated KOH ?

Aldehydes (not ketones) not containing $\mathrm{\alpha }$-hydrogen atoms undergo disproportionation in presence of conc. alkali.

The reaction is called Cannizzaro's reaction.

(2), (3). . .contain α - hydrogen atoms.

(4) … ketone

$\left(1\right) 2\mathrm{HCHO} \stackrel{\mathrm{conc}.\mathrm{KOH}}{\to } {\mathrm{HCOO}}^{-}{\mathrm{K}}^{+}+{\mathrm{CH}}_3\mathrm{OH}.$