(N/A) The reaction between $Propanal$ $(CH_3CH_2CHO)$ and $2-Methylpropanal$ $((CH_3)_2CHCHO)$ in the presence of dilute $NaOH$ is a $Cross-Aldol$ $Condensation$ reaction.
Since both aldehydes contain $\alpha$-hydrogens,a mixture of four different $\beta-hydroxy$ aldehydes (aldols) is formed:
$1$. Self-aldol condensation of $Propanal$: $3-hydroxy-2-methylpentanal$.
$2$. Self-aldol condensation of $2-Methylpropanal$: $3-hydroxy-2,2,4-trimethylpentanal$.
$3$. Cross-aldol condensation ($Propanal$ as nucleophile,$2-Methylpropanal$ as electrophile): $3-hydroxy-2,4-dimethylpentanal$.
$4$. Cross-aldol condensation ($2-Methylpropanal$ as nucleophile,$Propanal$ as electrophile): $3-hydroxy-2,2-dimethylpentanal$.
The reaction is known as $Cross-Aldol$ $Condensation$.