The product of the following reaction H2C=CH-CHO + NaBH4 /H2O is:

H2C=CH-CH2OH

Explanation:

Aldehydes are reduced to primary alcohols.

The first step in the reaction sequence is that the nucleophilic Hydrogen atom in the hydride reagent attacks the electrophilic Carbon in the polar carbonyl group of the aldehyde, there will now be a shift of electrons from the carbonyl to the Oxygen atom creating an intermediate metal alkoxide complex.

The reaction sequence is completed by a simple addition of a proton to the alkoxide oxygen which creates the primary alcohol product from the intermediate complex.