Two beakers of capacity 500 mL were taken. One of these beakersm labelled as ''A'', was filled with 400 mL water whereas the beaker labelled ''B'' was filled with 400 mL of 2 M solution of NaCl. At the same temperature both the bekers were place in closed containers of same material and same capacity as shown in Fig. At a given temperature, which of the following statement is correct about the vapour pressure of pure water and that of NaCl solution.

Options

A. Vapour pressure in container (A) is more than that in container (B).
B. Vapour pressure in container (A) is less than that in container (B).
C. Vapour pressure is equal in both the containers.
D. Vapour pressure in container (B) is twice the vapoure in container (A).

Answer

A

Explanation

Explanation : The vapour pressure is built up due to escaping tendencies of water molecules from the surface of the liquid. More the number of molecules on the surface of liquid greater would be the vapour pressure.
Since beaker A contains only water molecules at its surface it shows higher vapour pressure. But in beaker B containing NaCl solution, a fraction of surface area of the solution is occupied by NaCl molecules which are non - volatile in nature and have no escaping tendency.
This results into a decrease in the number of water molecules present in NaCl solution, thereby reducing its vapour pressure.