This reaction is known as aldol condensation.

C₂H₅ONa $$ \Rightarrow $$ C₂H₅O^- + Na⁺

The more the basic character of the leaving group, the lesser is the reactivity the basic character follows the order

NH₂^– > OR^– > RCOO^– > Cl^–

Hence, the relative reactivities of acyl compounds towards nucleophilic substitution follow the order

Acyl halides > Acid anhydride > Ester > Amide.

As the carbonyl carbon is electron deficient so most susceptible to attack by ncleophilic reagent or base.

Thus $$\alpha $$-hydrogen is the easily obstructed from ketones by a base.