How are aldehydes and ketones reduced to alcohols, and what reagents can be used for this reduction?

Aldehydes and ketones can be reduced to alcohols through catalytic or chemical reduction. Catalytic reduction involves using a metal catalyst, typically Raney nickel or platinum, under hydrogen gas (H₂) conditions. Alternatively, chemical reduction involves the use of reducing agents like sodium borohydride (NaBH₄) or lithium aluminum hydride (LiAlH₄). Sodium borohydride is milder and is commonly used for aldehyde and ketone reductions, while lithium aluminum hydride is a stronger reducing agent suitable for a wider range of carbonyl reductions, including those of carboxylic acids and esters. The reactions result in the addition of hydrogen, converting the carbonyl group to an alcohol.