What is life span of human RBC ?

Explanation

### Step-by-Step Solution:

1. **Understanding RBCs**: Red blood cells (RBCs), also known as erythrocytes, are the most abundant type of blood cells in the human body. They play a crucial role in the transport of respiratory gases, primarily oxygen and carbon dioxide.

2. **Average Count of RBCs**: In a healthy individual, the average count of RBCs is approximately 5 to 5.5 million cells per cubic millimeter (mm³) of blood. This indicates their abundance and importance in the circulatory system.

3. **Function of RBCs**: The primary function of RBCs is to carry oxygen from the lungs to the body's tissues and to transport carbon dioxide from the tissues back to the lungs. This is facilitated by hemoglobin, an iron-containing protein that gives RBCs their red color.

...