which has a higher density :oxygen gas or air ?

Answer 1

O2 has a mass of 32
N2 has a mass of 28
The air is about 20% O2 and 80% N2
It is a solution and is mixed.
The density of a gas depends on the pressure on it. The air is denser at sea level than on a mountain top.
D=m/v
Since the volume of a gas depends on its container, the density will vary depending on the container a gas is compressed onto.
Theyy say crawl along the floor to find fresh air in a fire. That is because warm air rises, oxygen is only minorly heavier.

Answer 2

Oxygen gas does. The molecular weight of oxygen is 32. The average molecular weight of 21% O2 and 78% N2 is 29.