What is the partial pressure of oxygen in a mixture that contains 0.30 moles of o2, 0.70 moles of n2, and 0.25 moles of ar with a total pressure of 1.1 atm?

moles gas / total moles = partial pressure gas / total pressure (Dalton's law)

Add up the moles to get the "total moles" (1.25), use "partial pressure gas" as a variable, and plug in all known information

0.30 / 1.25 = partial pressure O2 / 1.1

Solve for O2

partial pressure of O2 = 0.264 atm