Which of the following changes decrease the vapour pressure of water kept in a sealed vessel?
(i) Decreasing the quantity of water
(ii) Adding salt to water
(iii) Decreasing the volume of the vessel to one-half
(iv) Decreasing the temperature of water
The answer is the option (ii) Adding salt to the water, (iv) Decreasing the temperature of the water
Explanation: Adding salt to water decreases the surface area for a water molecule to vaporize, and hence vapour pressure of water also decreases.
Now, vapour pressure α temperature, hence, option (iv).