The vapour pressure of water at `20^@C` is 17.5 mmHg. Calculate mass of water per litre of air at `20^@C` and 45% relative humidity.

Explanation

To solve the problem, we need to calculate the mass of water per liter of air at 20°C and 45% relative humidity using the given vapor pressure of water at that temperature.

### Step-by-Step Solution:

1. **Understand the Concept of Relative Humidity**:
Relative Humidity (RH) is defined as the ratio of the partial pressure of water vapor (P_H2O) in the air to the saturation vapor pressure of water (P₀_H2O) at that temperature.
\[
\text{Relative Humidity} = \frac{P_{H2O}}{P^0_{H2O}} \times 100
...