Question

As we up the mountains the level of oxygen in the air ------------​

Answer 1

Answer: As we go up on a mountain the level of oxygen decrease

Explanation: As the bulk of the oxygen is present in troposphere (lowest part of the atmosphere and where we live) and most of the mountain peaks are above troposphere. Hence the oxygen decrease on higher altitude.

Answer 2

Answer:

decreases

Explanation:

As altitude increases, the amount of gas molecules in the air decreases—the air becomes less dense than air nearer to sea level. ... This is due to the low air pressure. Air expands as it rises, and the fewer gas molecules—including nitrogen, oxygen, and carbon dioxide—have fewer chances to bump into each other.