Give the conversion of the following:
$(i)$ $but-2-enal$ from $ethanal$
$(ii)$ $Methyl$ $benzoate$ from $benzaldehyde$

(N/A) $(i)$ $But-2-enal$ from $ethanal$:
$2CH_3CHO$ $\xrightarrow{dil. NaOH} CH_3-CH(OH)-CH_2-CHO$ $\xrightarrow{\Delta, -H_2O} CH_3-CH=CH-CHO$
$Ethanal$ undergoes aldol condensation in the presence of dilute $NaOH$ to form $3-hydroxybutanal$ (aldol),which upon heating loses a water molecule to form $but-2-enal$.
$(ii)$ $Methyl$ $benzoate$ from $benzaldehyde$:
$C_6H_5CHO$ $\xrightarrow{[O]} C_6H_5COOH$ $\xrightarrow{CH_3OH, conc. H_2SO_4, \Delta} C_6H_5COOCH_3$
$Benzaldehyde$ is first oxidized to $benzoic$ $acid$ using an oxidizing agent like $KMnO_4$ or $Tollens'$ reagent. Then,$benzoic$ $acid$ undergoes Fischer esterification with $methanol$ in the presence of concentrated $H_2SO_4$ to yield $methyl$ $benzoate$.