Dear Student,
Vapour pressure of a liquid is a measure of pressure of vapour against its solid or liquid counterpart within a closed system. In such case, equilibrium exist between liquid and its gaseous phase. The same equilibrium will be established if any container with different volume is used, although the rate of attaining the equilibrium may vary. As the vapour pressure is the pressure exerted by liquid at equilibrium, therefore it does not depend upon volume of container.