Which one of the following is a sex-linked disease?

Options

A. Nightblindness
B. Glaucoma
C. Haemophilia
D. All of these

Answer

To determine which of the following is a sex-linked disease, we need to understand what sex-linked diseases are and identify the options provided.

### Step-by-Step Solution:

1. **Understand Sex-Linked Diseases**:
- Sex-linked diseases are genetic disorders that are associated with genes located on the sex chromosomes (X or Y chromosomes). Most commonly, they are linked to the X chromosome.

2. **Identify Common Sex-Linked Diseases**:
- Some well-known sex-linked diseases include Hemophilia and Color Blindness, both of which are linked to the X chromosome.

3. **Analyze the Given Options**:
- The question mentions several conditions: Vitamin A deficiency, Glaucoma, Night blindness, and Hemophilia.
- Vitamin A deficiency is not a genetic condition; it is a nutritional deficiency.
- Glaucoma is an eye disorder but is not classified as a genetic or sex-linked disease.
- Night blindness can be genetic but is not specifically a sex-linked disease.
- Hemophilia, on the other hand, is a well-known sex-linked disorder, specifically linked to the X chromosome.

4. **Conclusion**:
- Based on the analysis, Hemophilia is the only condition listed that qualifies as a sex-linked disease.

### Final Answer:
**Hemophilia is a sex-linked disease.**