Which of the following is the best reducing agent to convert $RCOOH$ into $RCH_2OH$?

$B_2H_6$

The correct answer is Option (2) → $B_2H_6$

To reduce a carboxylic acid (RCOOH) to a primary alcohol (RCH₂OH), a strong reducing agent is required.

• • NaBH₄ → too mild; does not reduce carboxylic acids,  reduces aldehydes and ketones only

  • LiBH₄ → stronger than NaBH₄ but still not effective for RCOOH

  • H₂ / Pd → does not reduce carboxylic acids to alcohols

  • B₂H₆ → specifically and efficiently reduces RCOOH → RCH₂OH