Identify the correct statement :

Options

A. 0.1 M NaCl and 0.1 M glucose solution are isotonic
B. 0.1 M NaCl and 0.3 M glucose solution are isotonic.
C. The boiling point of 0.1 m aqueous urea solution is less than 0.1 m aqueous KCl solution.
D. The freezing point of 0.1 m glucose solution is less than 0.1 m KCl solution.

Answer

To solve the question of identifying the correct statement, we will analyze each of the four statements provided.

### Step-by-Step Solution:

1. **Statement 1: 0.1 molar NaCl and 0.1 molar glucose solution are isotonic.**
- **Analysis:** Isotonic solutions have the same osmotic pressure. The osmotic pressure (π) is given by the formula:
\[ \pi = i \cdot C \cdot R \cdot T \]
where \(i\) is the van 't Hoff factor (number of particles the solute dissociates into), \(C\) is the concentration, \(R\) is the gas constant, and \(T\) is the temperature in Kelvin.
- For NaCl, it dissociates into 2 ions (Na⁺ and Cl⁻), so \(i = 2\).
- For glucose (C₆H₁₂O₆), it does not dissociate, so \(i = 1\).
- Since both solutions have the same concentration (0.1 molar), the osmotic pressures will differ:
- NaCl: \( \pi = 2 \cdot 0.1 = 0.2 \)
- Glucose: \( \pi = 1 \cdot 0.1 = 0.1 \)
- Therefore, they are not isotonic. **This statement is incorrect.**

2. **Statement 2: 0.1 molar NaCl and 0.3 molar glucose are isotonic.**
- **Analysis:** Again, we calculate the osmotic pressures:
- For NaCl: \(i = 2\) and \(C = 0.1\), so \( \pi_{NaCl} = 2 \cdot 0.1 = 0.2 \).
- For glucose: \(i = 1\) and \(C = 0.3\), so \( \pi_{glucose} = 1 \cdot 0.3 = 0.3 \).
- Since \(0.2 \neq 0.3\), they are not isotonic. **This statement is incorrect.**

3. **Statement 3: The boiling point of 0.1 molal aqueous urea solution is less than 0.1 molal aqueous KCl solution.**
- **Analysis:** The boiling point elevation is given by:
\[ \Delta T_b = i \cdot K_b \cdot m \]
where \(K_b\) is the boiling point elevation constant and \(m\) is the molality.
- For urea: \(i = 1\) and \(m = 0.1\), so \( \Delta T_b = 1 \cdot K_b \cdot 0.1 \).
- For KCl: \(i = 2\) and \(m = 0.1\), so \( \Delta T_b = 2 \cdot K_b \cdot 0.1 \).
- Since \(2 \cdot K_b \cdot 0.1 > 1 \cdot K_b \cdot 0.1\), the boiling point of KCl solution is higher than that of urea solution.
- Therefore, the boiling point of urea is indeed less than that of KCl. **This statement is correct.**

4. **Statement 4: The freezing point of glucose is less than that of KCl.**
- **Analysis:** The freezing point depression is given by:
\[ \Delta T_f = i \cdot K_f \cdot m \]
- For glucose: \(i = 1\) and \(m = 0.1\), so \( \Delta T_f = 1 \cdot K_f \cdot 0.1 \).
- For KCl: \(i = 2\) and \(m = 0.1\), so \( \Delta T_f = 2 \cdot K_f \cdot 0.1 \).
- Since \(2 \cdot K_f \cdot 0.1 > 1 \cdot K_f \cdot 0.1\), the freezing point depression for KCl is greater, meaning the freezing point of KCl is lower than that of glucose.
- Therefore, the statement that the freezing point of glucose is less than that of KCl is incorrect. **This statement is incorrect.**

### Conclusion:
The only correct statement among the four is **Statement 3**: "The boiling point of 0.1 molal aqueous urea solution is less than 0.1 molal aqueous KCl solution."