I assume you mean at standard temperature and pressure. Use,
PV = nRT
(1 atm)(1 liter) = n(0.08206 L*atm/mol*K)(298.15 K)
n = 1/24.466
= 0.04 moles oxygen gas
--------------------------------
The temperature at which the solution boils is raised
Van der Waals forces
The total pressure of a mixture of gasses is the sum of the pressures of each gas in the mixture (Apex)