Ans: Vapor pressure is the pressure exerted by its vapor in phase equilibrium with its liquid at a given temperature.
The vapor pressure is equal to the saturation pressure at a given temperature (Pv=Psat).
The vapor pressure of water at 20°C is 2.34 kPa
If we keep a bucket of liquid water in a room at 20°C, the liquid water will keep evaporating into the room until the partial pressure of water vapor rises to 2.34 kPa in the room.
At this point, the phase equilibrium is established.