Answer
decrease
Work Step by Step
We know that $v_{rms}=\sqrt{\frac{3RT}{M}}$. This equation shows that $v_{rms}\propto \frac{1}{\sqrt M}$. Since oxygen molecules are massive compared to that of nitrogen, they move slower. Thus, at a particular height, the oxygen molecules will be smaller in quantity. We conclude that the ratio of oxygen to nitrogen molecules in the atmosphere decreases as we go up in altitude.
