Step-by-step explanation:
Aldol condensation refers to a reaction between an enolate ion or enol and a carbonyl compound to produce beta hydroxy aldehyde or beta hydroxy ketone. The initial step in a crossed aldol condensation is ketone deprotonates or enolizable aldehyde.
An enolizable ketone or aldehyde signifies that it should exhibit one or more alpha hydrogens. In the given case, only 3,3-dimethyl-2-butanone possess alpha hydrogen. Thus, it will get deprotonated by the base (hydroxide ion) in the initial step. In the succeeding step, it will be supplemented to the carbonyl carbon of the aldehyde. And in the ultimate step alkoxide gets protonated by water.