Biochemical Test for Reducing Sugars

Steps:

• Recall that glucose is a reducing sugar, which reacts with specific reagents to indicate its presence.
• Review each test's purpose: Benedict's for reducing sugars, Biuret for proteins, Ethanol emulsion for lipids, Iodine for starch.
• Match the test to glucose: only Benedict's targets monosaccharides like glucose.
• Confirm by the positive result: brick-red precipitate for glucose in Benedict's.

Why A is correct:

• Benedict's test uses alkaline copper(II) sulfate, which reduces to copper(I) oxide with glucose, forming a red precipitate (definition of reducing sugar test).

Why the others are wrong:

• B: Biuret test detects peptide bonds in proteins via violet color change.
• C: Ethanol emulsion test identifies insoluble lipids by milky emulsion formation.
• D: Iodine test reveals starch through blue-black complex formation.

Final answer: A