When a container is filled with 3 moles of helium gas, 2 moles of oxygen gas, and 1 mole of carbon dioxide gas, the pressure in the container is 786 kPa. What is the partial pressure of the oxygen gas?

A. 131 kPa

B. 262 kPa

C. 393 kPa

D. 786 kPa

The mole fraction of oxygen gas is 2/6 = 1/3, because there are 6 total moles of gas in the container. The partial pressure can be found by multiplying this mole fraction by the total pressure. So the answer is B. 262 kPA because 1/3 (786) = 262.