If the concentration of water vapour in the air is 1% and the total atmospheric pressure equals 1atm then the partial pressure of water vapour is?
A sample of O2 gas is collected over water at 23∘C at a barometric pressure of 751 mm Hg (vapour pressure of water at 23∘ C is 21 mm Hg). The partial pressure of O2 gas in the sample collected is____.