Fehling's test identifies aldehydes via orange precipitate

Steps:

• Observe orange precipitate in test tube Z, indicating a positive Fehling's test for reducing agents like aldehydes.
• Recall Fehling's reagent (alkaline Cu²⁺ solution) is reduced by aldehydes to red-orange Cu₂O precipitate.
• Examine options: only aldehydes among them reduce the reagent.
• Identify CH₃CHO as the aldehyde that fits the reaction.

Why B is correct:

• CH₃CHO (acetaldehyde) has the aldehydic group (-CHO) that undergoes oxidation, reducing Cu²⁺ to Cu₂O for the orange precipitate (RCHO + 2Cu²⁺ + 5OH⁻ → RCOO⁻ + Cu₂O + 3H₂O).

Why the others are wrong:

• A: CH₃CH₂OH (ethanol) is an alcohol, lacks reducing group, no reaction.
• C: CH₃COCH₃ (acetone) is a ketone, does not reduce Fehling's reagent.
• D: CH₃COOH (acetic acid) is a carboxylic acid, already oxidized, no precipitate.

Final answer: B