Explain why:
Acetaldehyde undergoes aldol con densation, but formaldehyde does not.

Explanation

In aldol condensation, such aldehydes and ketones which have at least one `alpha`- hydrogen undergo the reaction in presence of dilute alkali as catalyst to form `beta`-hydroxy aldehydes (aldol) or `beta`-hydroxy ketones (ketol), respectively. As benzaldehyde does not have an `alpha`-hydrogen, it does not undergo the aldol condensation reaction.