Iodine test is shown by

Options

A. Polypeptide
B. Glycogen
C. Starch
D. Glucose

Explanation

**Step-by-Step Solution:**

1. **Understanding the Iodine Test**: The iodine test is a qualitative test used to detect the presence of starch in a sample. When iodine solution (usually iodine dissolved in potassium iodide) is added to a sample containing starch, a blue-black color is produced.

2. **Identifying the Options**: The question provides four options: polypeptide, glycogen, starch, and glucose. We need to determine which of these substances gives a positive result in the iodine test.

3. **Analyzing Each Option**:
- **Polypeptide**: Polypeptides are chains of amino acids and do not react with iodine to produce a color change. Thus, they do not show a positive iodine test.
- **Glycogen**: Glycogen is a polysaccharide similar to starch, but it does not produce the characteristic blue-black color with iodine. It may give a brownish color but is not a definitive positive test.
- **Starch**: Starch is a polysaccharide made up of glucose units. It reacts with iodine to produce a blue-black color, indicating a positive iodine test.
- **Glucose**: Glucose is a simple sugar (monosaccharide) and does not react with iodine to produce any color. Therefore, it does not show a positive iodine test.

4. **Conclusion**: Based on the analysis, the only substance that shows a positive iodine test is starch.

**Final Answer**: The iodine test is shown by **starch**.

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