Haemoglobin is specifically described as a :

Options

A. protein
B. lipoprotein
C. enzyme
D. nucleolipid

Explanation

### Step-by-Step Solution:

1. **Understanding Hemoglobin**: Hemoglobin is a vital component of red blood cells (RBCs) that plays a crucial role in transporting oxygen from the lungs to the body's tissues and returning carbon dioxide from the tissues back to the lungs.

2. **Identifying the Nature of Hemoglobin**: Hemoglobin is primarily composed of proteins. It is an iron-containing protein, which gives it the ability to bind with oxygen. This binding is reversible, allowing hemoglobin to pick up oxygen in the lungs and release it in the tissues.

3. **Analyzing the Options**:
- **Protein**: Hemoglobin is indeed a protein, specifically a globular protein with a quaternary structure made up of four subunits.
- **Lipoprotein**: This term refers to proteins that are combined with lipids. Hemoglobin does not have a lipid component, so this option is incorrect.
- **Enzyme**: Enzymes are biological catalysts that speed up chemical reactions. Hemoglobin does not catalyze reactions; it simply transports gases, making this option incorrect.
- **Nucleolipid**: This term suggests a combination of nucleic acids and lipids. Hemoglobin does not contain nucleic acids, so this option is also incorrect.

4. **Conclusion**: Based on the analysis, hemoglobin is best described as a **protein**. It is an iron-containing protein that functions as a respiratory pigment, facilitating the transport of oxygen in the blood.

### Final Answer:
**Haemoglobin is specifically described as a protein.**

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