A 10 liter flask at 298 K contains a gaseous mixture of O2 and CO2 at 1 atmosphere. Which statement is true for the partial pressures of O2 and CO2 if 0.2 mole of O2 is present in the flask? (Given the universal gas constant R = 0.082 L∙atm/K∙mol)

Answer 1

You didn't give the options for an answer but here is how you determine the parital pressure of O2. It can also be solve another way by going through mole fractions.
Use PV = nRT. Plug in V, R, and T (in kelvin remember) and use 0.2 mole for n. Solve for P