Which of the following gives positive Fehling solution test?

Options

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

Explanation

To determine which of the following compounds gives a positive Fehling solution test, we need to analyze each option based on the presence of a free aldehyde group (CHO group), as this is what Fehling's test detects.

### Step-by-Step Solution:

1. **Understanding Fehling's Test**:
- Fehling's test is used to identify the presence of aldehydes. The test involves two solutions, Fehling's A (copper sulfate solution) and Fehling's B (alkaline tartrate solution). When an aldehyde is present, it reduces the blue copper(II) ions (Cu²⁺) to red precipitate copper(I) oxide (Cu₂O) upon heating.

2. **Analyzing Each Option**:
- **Option 1: Protein**:
- Proteins are polymers of amino acids and do not contain free aldehyde groups. They are made up of amino (-NH₂) and carboxyl (-COOH) functional groups. Therefore, proteins do not give a positive Fehling test.
- **Option 2: Sucrose**:
- Sucrose is a disaccharide formed from glucose and fructose. It does not have a free aldehyde group due to the glycosidic bond between the two monosaccharides. Thus, sucrose will not give a positive Fehling test.
- **Option 3: Glucose**:
- Glucose is a monosaccharide and an aldohexose, meaning it has a free aldehyde group. This allows glucose to reduce the copper ions in Fehling's solution, resulting in a positive test. Therefore, glucose will give a positive Fehling test.
- **Option 4: Fat**:
- Fats (lipids) do not contain free aldehyde groups. They are primarily composed of fatty acids and glycerol. Hence, fats will not give a positive Fehling test.

3. **Conclusion**:
- Among the given options, only **glucose** (Option 3) contains a free aldehyde group and will give a positive Fehling solution test.

### Final Answer:
**Glucose (Option 3) gives a positive Fehling solution test.**

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