The major product formed when propanal is treated with a catalytic amount of NaOH and CH3CH2I is 2-ethoxypropanal. The reaction proceeds through a nucleophilic addition mechanism. Here is the stepwise mechanism:1. Deprotonation: The hydroxide ion OH- from NaOH acts as a base and abstracts a proton from the -carbon of propanal, forming an enolate ion and water. Propanal + OH- Enolate ion + H2O2. Nucleophilic attack: The enolate ion, being a strong nucleophile, attacks the electrophilic carbon of the CH3CH2I molecule, displacing the iodide ion I- and forming a new C-O bond. Enolate ion + CH3CH2I 2-Ethoxypropanal + I-Overall, the reaction can be summarized as: Propanal + NaOH + CH3CH2I 2-Ethoxypropanal + NaI + H2O