AIIMS 2019 Chemistry Selective Reduction MCQ Question

NaBH₄ (sodium borohydride) is a selective reducing agent that effectively reduces aldehydes (RCHO) and ketones (RC(=O)R') to their corresponding alcohols (RCH₂OH and R'CHOH, respectively) due to the presence of carbonyl (C=O) functional groups. However, it does not reduce esters (RCOOR') because the reaction requires breaking a C–O bond, which NaBH₄ cannot effectively do. Similarly, alkenes (RCH=CHR') are not affected by NaBH₄ since they lack a carbonyl group that can be reduced to an alcohol. Thus, option D (Ester) is correct as it is not reduced by NaBH₄.