Question

what is the partial pressure of 02 collected over water at 25 degree C and 630 torr (vapor pressure of H20 at 25 degree C is 23.8 torr)

Answer 1

Dalton's Law tell us that the total pressure is the sum of the partial pressures of the gases.
Ptotal = PO2 + PH2O
630 torr = PO2 + 23.0
Solve for PO2.