Explain the cross aldol condensation reaction.

(N/A) When an aldol condensation reaction is carried out between two different aldehyde or ketone compounds,it is known as a cross aldol condensation. If both compounds possess at least one $\alpha$-hydrogen atom,the reaction between them yields a mixture of $4$ different products.
For example,the reaction between ethanal $(CH_3CHO)$ and propanal $(CH_3CH_2CHO)$ in the presence of dilute $NaOH$ followed by heating gives the following four products:
$(i)$ Self-aldol condensation of two molecules of ethanal: $CH_3-CH=CH-CHO$ (but$-2-$enal).
$(ii)$ Self-aldol condensation of two molecules of propanal: $CH_3CH_2-CH=C(CH_3)-CHO$ ($2$-methylpent$-2-$enal).
$(iii)$ Cross-aldol condensation where the $\alpha$-hydrogen of propanal reacts with the carbonyl oxygen of ethanal: $CH_3-CH=C(CH_3)-CHO$ ($2$-methylbut$-2-$enal).
$(iv)$ Cross-aldol condensation where the $\alpha$-hydrogen of ethanal reacts with the carbonyl oxygen of propanal: $CH_3CH_2-CH=CH-CHO$ (pent$-2-$enal).
The acidity of $\alpha$-hydrogen is due to the strong electron-withdrawing effect of the carbonyl group and the resonance stabilization of the resulting enolate ion (conjugated base).