The rarest leucocyte of human blood is

Options

A. Basophil
B. Monocyte
C. Neutrophil
D. Eosinophil

Answer

**Step-by-Step Solution:**

1. **Understanding Leukocytes**: Leukocytes, also known as white blood cells (WBCs), are a crucial component of the immune system. They help the body fight infections and other diseases.

2. **Types of Leukocytes**: There are two main categories of leukocytes: granular and agranular.
- Granular leukocytes include neutrophils, eosinophils, and basophils.
- Agranular leukocytes include lymphocytes and monocytes.

3. **Percentage Composition**: Each type of leukocyte has a different percentage representation in human blood:
- Neutrophils: Approximately 62%
- Eosinophils: Approximately 2.3%
- Basophils: Approximately 0.4%
- Monocytes: Approximately 5-10%
- Lymphocytes: Approximately 20-40%

4. **Identifying the Rarest Leukocyte**: From the percentages listed, basophils have the lowest percentage at 0.4%. This indicates that basophils are the rarest type of leukocyte in human blood.

5. **Conclusion**: Therefore, the rarest leukocyte of human blood is basophil.

**Final Answer**: The rarest leucocyte of human blood is **basophil**.

---