Assertion (A): The osmotic pressure of `0.1 M` urea solution is less than `0.1 M NaCl` solution.
Reason (R ): Osmotic pressure is not a colligative property.

Options

A. If both `(A)` and `(R )` are correct, and `(R )` is the correct explanation of `(A)`.
B. If both `(A)` and `(R )` are correct, but `(R )` is not the correct explanation of `(A)`.
C. If `(A)` is correct, but `(R )` is incorrect.
D. If `(A)` is correct, but `(R )` is correct.

Explanation

To solve the question, we need to analyze the two statements: the assertion (A) and the reason (R).

### Step 1: Analyze the Assertion (A)
The assertion states that the osmotic pressure of a `0.1 M` urea solution is less than that of a `0.1 M NaCl` solution.

- **Osmotic Pressure Formula**: The osmotic pressure (π) can be calculated using the formula:
\[ \pi = iCRT \]
where:
- \( i \) = van 't Hoff factor (number of particles the solute dissociates into)
- \( C \) = molarity of the solution
- \( R \) = gas constant
- \( T \) = temperature in Kelvin

- **Urea (NH2CO-NH2)**: Urea is a non-electrolyte and does not dissociate into ions. Therefore, its van 't Hoff factor \( i \) is 1.

- **Sodium Chloride (NaCl)**: NaCl is a strong electrolyte and dissociates into two ions (Na⁺ and Cl⁻) in solution. Therefore, its van 't Hoff factor \( i \) is 2.

- **Comparison**:
- For urea:
\[ \pi_{\text{urea}} = 1 \times 0.1 \times R \times T \]
- For NaCl:
\[ \pi_{\text{NaCl}} = 2 \times 0.1 \times R \times T \]

Since \( \pi_{\text{NaCl}} \) is greater than \( \pi_{\text{urea}} \), the assertion is **true**.

### Step 2: Analyze the Reason (R)
The reason states that osmotic pressure is not a colligative property.

- **Definition of Colligative Properties**: Colligative properties depend on the number of solute particles in a solution, not on the identity of the solute. Osmotic pressure is indeed a colligative property because it depends on the number of solute particles (which is influenced by the van 't Hoff factor).

Thus, the reason is **false**.

### Conclusion
- The assertion (A) is true: The osmotic pressure of `0.1 M` urea is less than that of `0.1 M NaCl`.
- The reason (R) is false: Osmotic pressure **is** a colligative property.

### Final Answer
The correct answer is that the assertion is correct, but the reason is incorrect.

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