In this reaction, when 2-Methylbutanal reacts with the given reagent NaBH₄, then the double bond between carbon and oxygen gets to break down in the above aldehyde compound, where carbon has positive charge and oxygen will have a negative charge on them. So, H⁺ gets placed on the carbon to complete its octet and H⁺ gets substituted on O^- to form OH, i.e, an alcohol. Thus we get 2-Methylbutan-1-ol as a product.