Hello candidate,

Solubility of oxygen in pure water is given as 43 milligrams per litre of water, which means that in one litre of water 43 grams of oxygen is dissolved.

The pressure is 20 torr and the temperature is 20 degrees celsius, so using the real state equation of gas- PV= nRT, we can find out the number of moles and subsequently the amount of oxygen required from the given set of values.

Hope it was informational!!