Assertion (A): The boiling point of 0.1 M solution is less that that of 0.1 M'KCl solution.
Reason (R): Elevation of boiling point is directly proportional to the number of species present in the solution.

Options

A. Both A and Rare true and R is the correct ex planation of A
B. Both A and Rare true but R is not the correct explanation of A
C. A is true but R is false
D. A is false but R is true

Explanation

To solve the question, we need to analyze the assertion and reason provided:

**Assertion (A):** The boiling point of a 0.1 M solution of urea is less than that of a 0.1 M KCl solution.
**Reason (R):** Elevation of boiling point is directly proportional to the number of species present in the solution.

### Step-by-Step Solution:

1. **Understanding Colligative Properties:**
- Colligative properties depend on the number of solute particles in a solution rather than the type of particles. The elevation of boiling point is one such property.

2. **Boiling Point Elevation Formula:**
- The formula for boiling point elevation (ΔT_b) is given by:
\[ \Delta T_b = K_b \cdot m \cdot i \]
where:
- \( K_b \) = ebullioscopic constant of the solvent,
- \( m \) = molality of the solution,
- \( i \) = van 't Hoff factor (number of particles the solute dissociates into).

3. **Analyzing Urea and KCl:**
- Urea is a non-electrolyte, which means it does not dissociate in solution. Therefore, for urea:
- \( i = 1 \)
- KCl is an electrolyte that dissociates into two ions (K⁺ and Cl⁻) when dissolved in water. Therefore, for KCl:
- \( i = 2 \)

4. **Calculating the Effect on Boiling Point:**
- For both solutions, the molarity is the same (0.1 M).
- For urea:
\[ \Delta T_b \text{ (urea)} = K_b \cdot 0.1 \cdot 1 = 0.1 K_b \]
- For KCl:
\[ \Delta T_b \text{ (KCl)} = K_b \cdot 0.1 \cdot 2 = 0.2 K_b \]

5. **Comparison of Boiling Points:**
- Since the boiling point elevation for KCl is greater than that for urea, the boiling point of the KCl solution is higher.
- Therefore, the boiling point of the 0.1 M urea solution is indeed less than that of the 0.1 M KCl solution.

6. **Conclusion:**
- The assertion (A) is true.
- The reason (R) is also true and correctly explains the assertion.
- Thus, both the assertion and reason are true, and the reason is a correct explanation of the assertion.

### Final Answer:
Both the assertion and reason are true, and the reason correctly explains the assertion.

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