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

Which of the following has higher vapour pressure? (mercury, water)

A cylinder fitted with a movable piston contains liquid water in equilibrium with water vapour at 25^(@)C . Which of the following operation results in a decrease in the equilibrium vapour pressure at 25^(@) C?

What mass of urea be dissolved in 171 g of water so as to decrease the vapour pressure of water by 5% ?