Assertion: Decrease in the vapour pressure of water by adding 1 mol of sucrose to one kg of water is higher to that produced by adding 1 mol of urea to the same quantity of water at the same temperature .
Reason : Molecular mass of sugar is less than that of urea .

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false
D. If both assertion and reason are false

Explanation

To solve the question, we need to analyze both the assertion and the reason provided in the statement.

### Step 1: Understand the Assertion
The assertion states that the decrease in vapor pressure of water by adding 1 mole of sucrose to 1 kg of water is higher than that produced by adding 1 mole of urea to the same quantity of water at the same temperature.

**Hint:** Consider the colligative properties of solutions, particularly how the number of solute particles affects vapor pressure.

### Step 2: Analyze the Colligative Properties
The decrease in vapor pressure is a colligative property, which means it depends on the number of solute particles in the solution rather than their identity. For non-electrolytes like sucrose and urea, the van 't Hoff factor (i) is 1 for both, since they do not dissociate into ions.

**Hint:** Recall that the formula for the decrease in vapor pressure is related to the mole fraction of the solute.

### Step 3: Compare Sucrose and Urea
Both sucrose and urea are non-electrolytes and do not dissociate in solution. Therefore, when 1 mole of each is added to 1 kg of water, the number of solute particles is the same (1 mole). This means that the decrease in vapor pressure will be the same for both sucrose and urea.

**Hint:** Think about how the number of particles influences the vapor pressure and remember that both solutes behave similarly in this context.

### Step 4: Evaluate the Reason
The reason states that the molecular mass of sugar (sucrose) is less than that of urea. However, the molecular mass of sucrose is approximately 342 g/mol, while that of urea is about 60 g/mol. Therefore, this statement is incorrect.

**Hint:** Check the molecular weights of both compounds to confirm which one is heavier.

### Step 5: Conclusion
Since both the assertion and the reason are false, the correct answer is that both the assertion and reason are incorrect.

**Final Answer:** The correct option is 4: Both assertion and reason are false.