(N/A) $(i)$ $\text{Conversion of Ethanal to Pent-3-en-2-one}$:
$\text{Ethanal } (CH_3CHO) \text{ reacts with Propanone } (CH_3COCH_3) \text{ in the presence of dilute } NaOH \text{ (Cross-Aldol condensation) to form 4-hydroxypentan-2-one.}$
$CH_3CHO + CH_3COCH_3 \xrightarrow{\text{dil. } NaOH} CH_3CH(OH)CH_2COCH_3$
$\text{Dehydration of 4-hydroxypentan-2-one by heating gives Pent-3-en-2-one.}$
$CH_3CH(OH)CH_2COCH_3 \xrightarrow{\Delta, -H_2O} CH_3CH=CHCOCH_3$
$(ii)$ $\text{Conversion of Ethanal to Pent-2-enal}$:
$\text{Ethanal } (CH_3CHO) \text{ undergoes Cross-Aldol condensation with Propanal } (CH_3CH_2CHO) \text{ in the presence of dilute } NaOH \text{ to form 3-hydroxypentanal.}$
$CH_3CH_2CHO + CH_3CHO \xrightarrow{\text{dil. } NaOH} CH_3CH_2CH(OH)CH_2CHO$
$\text{Dehydration of 3-hydroxypentanal by heating gives Pent-2-enal.}$
$CH_3CH_2CH(OH)CH_2CHO \xrightarrow{\Delta, -H_2O} CH_3CH_2CH=CHCHO$