Main cation of extracelluar fluid is

Options

A. Iron
B. Potassium
C. Calcium
D. Sodium

Answer

### Step-by-Step Solution:

1. **Understanding Extracellular Fluid (ECF)**:
- Extracellular fluid refers to all body fluids outside the cells. It constitutes about one-third of the total body fluids. The two main components of ECF are interstitial fluid (the fluid between cells) and plasma (the liquid component of blood).

2. **Identifying Cations in ECF**:
- Cations are positively charged ions. In the context of extracellular fluid, several cations are present, including sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), and iron (Fe²⁺).

3. **Determining the Main Cation**:
- Among the cations present in extracellular fluid, sodium is recognized as the primary cation. It plays a crucial role in maintaining fluid balance, osmotic pressure, and is vital for nerve and muscle function.

4. **Evaluating the Options**:
- Given the options: Iron, Potassium, Calcium, Sodium:
- **Iron**: Incorrect, as it is primarily associated with hemoglobin in red blood cells and not a major component of ECF.
- **Potassium**: Incorrect, as it is the main cation of intracellular fluid, not extracellular fluid.
- **Calcium**: Incorrect, it is present in ECF but not as the main cation.
- **Sodium**: Correct, as it is the main cation of extracellular fluid.

5. **Conclusion**:
- The main cation of extracellular fluid is **Sodium (Na⁺)**.