Answer
The partial pressure of the oxygen gas is $321 mm Hg$
Work Step by Step
We can find the partial pressure by using Dalton's Law of Partial Pressures which states the total pressure of a mixture of gases is simply the summation of the partial pressure of the gases;
If the total pressure is $752 mmHg$ and the partial pressure of the helium gas is $234 mmHg$, and for nitrogen is $197 mmHg $, then the partial pressure of the oxygen gas is $752-197-234 = 321 $ mmHg because $197 + 234 + 321 = 752$ mmHg.
