Aqueous solution of urea is 20% by mass of solution. Then the percentage of urea by mass of solvent is

Options

A. 0.2
B. 0.25
C. 0.4
D. 0.8

Answer

To find the percentage of urea by mass of the solvent in a 20% by mass aqueous solution of urea, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Problem**: We have a solution that is 20% urea by mass. This means that in every 100 grams of the solution, 20 grams is urea, and the rest (80 grams) is the solvent (water).

2. **Identify the Mass of Solvent**: Since the total mass of the solution is 100 grams and the mass of urea is 20 grams, the mass of the solvent (water) can be calculated as:
\[ \text{Mass of solvent} = \text{Total mass of solution} - \text{Mass of urea} = 100 \, \text{g} - 20 \, \text{g} = 80 \, \text{g} \]

3. **Calculate the Percentage of Urea by Mass of Solvent**: To find the percentage of urea by mass of the solvent, we use the formula:
\[ \text{Percentage of urea by mass of solvent} = \left( \frac{\text{Mass of urea}}{\text{Mass of solvent}} \right) \times 100 \]
Substituting the values we found:
\[ \text{Percentage of urea by mass of solvent} = \left( \frac{20 \, \text{g}}{80 \, \text{g}} \right) \times 100 \]

4. **Perform the Calculation**:
\[ \text{Percentage of urea by mass of solvent} = \left( \frac{20}{80} \right) \times 100 = 0.25 \times 100 = 25\% \]

### Final Answer:
The percentage of urea by mass of the solvent is **25%**.

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