The concentration unit, independent of temperature would be

Options

A. molality
B. molarity
C. normality
D. weight per volume

Explanation

To determine which concentration unit is independent of temperature, we will analyze the different concentration units: molality, molarity, normality, and weight by volume.

### Step-by-Step Solution:

1. **Understanding Molality**:
- Molality (m) is defined as the number of moles of solute per kilogram of solvent.
- Formula:
\[ \text{Molality (m)} = \frac{\text{mass of solute (g)}}{\text{molar mass of solute (g/mol)}} \times \frac{1000}{\text{mass of solvent (kg)}} \]
- Since both the mass of solute and the mass of solvent are constants (they do not change with temperature), molality is independent of temperature.

2. **Understanding Molarity**:
- Molarity (M) is defined as the number of moles of solute per liter of solution.
- Formula:
\[ \text{Molarity (M)} = \frac{\text{number of moles of solute}}{\text{volume of solution (L)}} \]
- The volume of the solution is temperature-dependent because it can expand or contract with temperature changes. Therefore, molarity is dependent on temperature.

3. **Understanding Normality**:
- Normality (N) is defined as the number of equivalents of solute per liter of solution.
- Formula:
\[ \text{Normality (N)} = \frac{\text{mass of solute (g)}}{\text{volume of solution (L)} \times \text{equivalent weight of solute (g/equiv)}} \]
- Similar to molarity, the volume of the solution is temperature-dependent, making normality also dependent on temperature.

4. **Understanding Weight by Volume**:
- Weight by volume percentage is defined as the mass of solute in grams per 100 mL of solution.
- Formula:
\[ \text{Weight by Volume (\% w/v)} = \frac{\text{weight of solute (g)}}{\text{volume of solution (mL)}} \times 100 \]
- The volume term in this calculation is also temperature-dependent, which means weight by volume is temperature-dependent as well.

5. **Conclusion**:
- After analyzing all the concentration units, we find that only **molality** is independent of temperature.

### Final Answer:
The concentration unit independent of temperature is **molality**.