Question

Which one of the following gives positive Fehling's solution test?

• A. Sucrose
• B. Glucose
• C. Fats
• D. Protein

Answer 1

The Correct Option is B

To determine which substance among the given options gives a positive Fehling's solution test, we need to understand what Fehling's test is used for.

Fehling's solution is a chemical test used to differentiate between water-soluble carbohydrates and ketones. It is specifically used to test for the presence of reducing sugars. Reducing sugars are sugars that can donate electrons to another chemical in a reduction reaction, typically sugars with a free aldehyde or ketone group.

1. Glucose: Glucose is an aldose, meaning it contains an aldehyde group. As a reducing sugar, it reacts with Fehling's solution to give a positive test, forming a red precipitate of copper(I) oxide.
2. Sucrose: Sucrose is a disaccharide composed of glucose and fructose. It is a non-reducing sugar because the glycosidic bond between the glucose and fructose units prevents it from having a free aldehyde or ketone group. Therefore, it gives a negative result in Fehling's test.
3. Fats: Fats are composed of long-chain fatty acids esterified to glycerol and do not contain any reducing groups that can react with Fehling's solution. Hence, they give a negative result.
4. Protein: Proteins are made up of amino acids linked by peptide bonds. They do not have free aldehyde or ketone groups, so they would also give a negative result in Fehling's test.

Based on this analysis, the correct answer is Glucose, as it gives a positive Fehling's solution test due to its ability to act as a reducing sugar.