An air-water vapour mixture has a dry-bulb temperature of 333 k and a dew-point temperature of 313 k. the total pressure is 101.3 kpa and the vapour pressure of water at 313 k is 7.3 kpa and that at 333 k is 19.91 kpa. the humidity of air expressed as kg of water vapour per kg of dry air is (a) 0.048 (b) 0.079 (c) 0.122 (d) 0.152