1.

Which of the following changes decrease the vapour pressure of water kept in a sealed vessel ?

Answer»

Decreasing the QUANTITY of water
Adding salt to water
Decreasing the volume of the vessel to ONE half
Decreasing the temperature of water

Solution :When salt is added, less surface area is left for the water molecules to VAPORISE as salt molecules occupy the position of water molecules on the surface. Thus, VAPOUR pressure of water decreases.
However, vapour pressure also decreases with DECREASE in temperature as kinetic energy of the molecules decrease.


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