A vessel contains a small amount of water at `0^(@)C`. If the air in the vessel is rapidly pumped out, it causes freezing of the water. Why? What percentage of the water in the container can be frozen by this method? Latent heat of vaporization and fusion are `L_(V) = 540 cal g^(-1)` and `L_(f) = 80 cal g^(-1)` respectively.