Molality is expressed in units of

Options

A. `mol kg^(-1)`
B. `mol L^(-1)`
C. `mol L^(-1)s^(-1)`
D. `mol g^(-1)s^(-1)`

Answer

To determine the units of molality, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Molality**:
- Molality (m) is defined as the number of moles of solute per kilogram of solvent.

2. **Formula for Molality**:
- The formula for calculating molality is:
\[ \text{Molality (m)} = \frac{\text{Number of moles of solute}}{\text{Mass of solvent in kg}} \]

3. **Identifying Units**:
- The unit for the number of moles of solute is "mole" (mol).
- The unit for the mass of solvent is "kilogram" (kg).

4. **Combining Units**:
- Therefore, the units of molality can be expressed as:
\[ \text{Units of molality} = \frac{\text{moles}}{\text{kg}} = \text{mol/kg} \]

5. **Alternative Representation**:
- This can also be written as:
\[ \text{mol kg}^{-1} \]

6. **Conclusion**:
- Thus, the correct unit for molality is "mole per kilogram" or "mol/kg".

### Final Answer:
- The unit of molality is **mole per kilogram (mol/kg)**.