Concept:In aldol condensation, the enolate ion of one aldehyde attacks the carbonyl carbon of another aldehyde, forming a β-hydroxy aldehyde which dehydrates to an α,β-unsaturated aldehyde.Explanation:Ethanal is CH3​CHO.Propanal is CH3​CH2​CHO.In cross aldol condensation, both aldehydes can act as the enolate donor.When ethanal gives the enolate and attacks propanal, dehydration gives pent-2-enal:CH3​CH2​CHO+CH3​CHOOH−​CH3​CH2​CH=CHCHOThis product is pent-2-enal.When propanal gives the enolate and attacks ethanal, dehydration gives 2-methylbut-2-enal:CH3​CHO+CH3​CH2​CHOOH−​CH3​CH=C(CH3​)CHOThis product is 2-methylbut-2-enal.Hence the pair of cross condensation products is 2-methylbut-2-enal and pent-2-enal.Answer:2-methylbut-2-enal and pent-2-enalCorrect option: C.