The average concentration of `Na^(+)` ion in human body is 3.0 to 4.0
gm per litre. The molarity of `Na^(+)` ion is about.

Answer

To find the molarity of `Na^(+)` ions in the human body given the average concentration of 3.0 to 4.0 grams per liter, we can follow these steps:

### Step-by-Step Solution:

1. **Determine the Average Concentration**:
- The average concentration of `Na^(+)` ions is given as a range of 3.0 to 4.0 grams per liter.
- To find the average, we calculate:
\[ \text{Average concentration} = \frac{3.0 \, \text{g/L} + 4.0 \, \text{g/L}}{2} = \frac{7.0 \, \text{g/L}}{2} = 3.5 \, \text{g/L} \]

2. **Calculate the Number of Moles**:
- To find the number of moles of `Na^(+)`, we use the formula:
\[ \text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}} \]
- The molar mass of sodium (Na) is approximately 23 g/mol. Therefore, we calculate:
\[ \text{Moles of Na} = \frac{3.5 \, \text{g}}{23 \, \text{g/mol}} \approx 0.1522 \, \text{mol} \]

3. **Calculate the Molarity**:
- Molarity (M) is defined as the number of moles of solute per liter of solution. Since we have the mass concentration in grams per liter and we calculated the moles, we can find the molarity:
\[ \text{Molarity} = \frac{\text{Moles}}{\text{Volume (L)}} \]
- Here, the volume is 1 liter, so:
\[ \text{Molarity} = \frac{0.1522 \, \text{mol}}{1 \, \text{L}} \approx 0.1522 \, \text{M} \]

4. **Final Answer**:
- The approximate molarity of `Na^(+)` ions in the human body is about **0.15 M**.