At a certain temperature, the vapour pressure of water is 90 mm. At the same temperature the vapour pressure of a solution containing a non - volatile solute is 81 mm. The relative lowering of vapour pressure is

Options

A. 9
B. `0.9`
C. 10
D. `0.1`

Explanation

To find the relative lowering of vapor pressure, we can follow these steps:

### Step 1: Identify the given values
- The vapor pressure of pure water (P₀) = 90 mm
- The vapor pressure of the solution (P) = 81 mm

### Step 2: Calculate the lowering of vapor pressure
Lowering of vapor pressure can be calculated using the formula:
\[ \text{Lowering of Vapor Pressure} = P₀ - P \]

Substituting the values:
\[ \text{Lowering of Vapor Pressure} = 90 \, \text{mm} - 81 \, \text{mm} = 9 \, \text{mm} \]

### Step 3: Calculate the relative lowering of vapor pressure
Relative lowering of vapor pressure is given by the formula:
\[ \text{Relative Lowering of Vapor Pressure} = \frac{\text{Lowering of Vapor Pressure}}{P₀} \]

Substituting the values:
\[ \text{Relative Lowering of Vapor Pressure} = \frac{9 \, \text{mm}}{90 \, \text{mm}} \]

### Step 4: Simplify the fraction
\[ \text{Relative Lowering of Vapor Pressure} = \frac{1}{10} \]

### Final Answer
The relative lowering of vapor pressure is \( \frac{1}{10} \).

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