Molality is expressed in units of

Options

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

Answer

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

### Step-by-Step Solution:

1. **Understand the Definition of Molality**:
- Molality (m) is defined as the number of moles of solute present in 1 kilogram of solvent.

2. **Identify the Components**:
- The two components involved in the definition are:
- Number of moles of solute (unit: moles)
- Mass of solvent (unit: kilograms)

3. **Write the Formula for Molality**:
- The formula for calculating molality is given by:
\[ m = \frac{\text{Number of moles of solute}}{\text{Mass of solvent in kg}} \]

4. **Substitute the Units into the Formula**:
- The unit of the number of moles of solute is "mole" (mol).
- The unit of the mass of solvent is "kilogram" (kg).
- Therefore, the units for molality can be expressed as:
\[ \text{Units of molality} = \frac{\text{moles}}{\text{kg}} = \text{mol/kg} \]

5. **Conclusion**:
- The unit of molality is "mole per kilogram" (mol/kg).

### Final Answer:
- Molality is expressed in units of **mole per kilogram (mol/kg)**.