In a test for reducing sugar, the food substance is usually warmed with

Step 1: Analyze the question The question asks which reagent is used, with warming, to test for a reducing sugar (such as glucose, fructose, maltose).

Step 2: The concept Reducing sugars have free aldehyde or ketone groups that can reduce copper(II) ions (Cu²⁺, blue) to copper(I) oxide (Cu₂O, brick-red precipitate). Two reagents are commonly used:

• Benedict's solution (copper(II) sulphate + sodium carbonate + sodium citrate): the food is warmed (heated in a water bath) with it.
• Fehling's solution: works the same way.

Step 3: Check each option

• A. Benedict's solution: Correct. Warm the food sample with it. A colour change from blue → green → yellow/orange → brick-red precipitate shows a reducing sugar is present.
• B. Millon's reagent: Used for proteins (gives a red/pink colour).
• C. Sodium hydroxide: Used with dilute copper(II) sulphate in the Biuret test for proteins, not for reducing sugar on its own.
• D. Sudan III: Used to test for fats and oils (red stain).
• E. 1% copper II sulphate solution: Used in the Biuret test for protein. It is not the reagent for reducing sugar, because without the alkaline/citrate mixture of Benedict's it will not work in the same way.

Step 4: Answer The food substance is warmed with Benedict's solution, so the answer is A.

Exam tip: Remember the pairings:

• Benedict's → Brick-red (reducing sugar, needs heat)
• Millon's → Meat (protein)
• Sudan III → Simplest fats (oils/fats)
• Iodine → Starch (blue-black)