Trouton's rule gives the relation between

Options

A. `T_(b)` and `T_(C)`
B. `T_(b)` and critical pressure
C. Enthalpy of vaporisation and boiling point
D. Normal boiling point and boiling point

Explanation

**Step-by-Step Solution:**

1. **Understanding Trouton's Rule**: Trouton's rule states that the enthalpy of vaporization (ΔH_vap) of a liquid is approximately proportional to its boiling point (T_b). The relationship can be expressed mathematically as:
\[ \frac{\Delta H_{vap}}{T_b} \approx 21 \, \text{cal K}^{-1} \text{mol}^{-1} \]

2. **Identifying the Variables**: In this equation:
- ΔH_vap = Enthalpy of vaporization
- T_b = Boiling point of the liquid

3. **Rearranging the Equation**: From the equation, we can rearrange it to show that:
\[ \Delta H_{vap} \approx T_b \times 21 \, \text{cal K}^{-1} \text{mol}^{-1} \]
This indicates that the enthalpy of vaporization is directly related to the boiling point of the substance.

4. **Analyzing the Options**: The question asks for the relationship that Trouton's rule gives. The options typically include various thermodynamic properties. We need to identify which option correctly describes the relationship stated in Trouton's rule.

5. **Selecting the Correct Option**: Based on the analysis:
- Option A: Normal boiling point and critical temperature (not directly related)
- Option B: Normal boiling point and critical pressure (not directly related)
- Option C: Enthalpy of vaporization and boiling point (this is the correct relationship)
- Option D: Normal boiling point and boiling point (not a valid relationship)

6. **Conclusion**: The correct answer is Option C, which states that Trouton's rule gives the relationship between the enthalpy of vaporization and the boiling point.

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