oxygen
Helium is lighter (less dense) than oxygen & nitrogen.
Nitrogen is four fifths of the air so their densities are very similar. Pure nitrogen is slightly less dense than air.
6a-4
10x - 4
4n - 1
4n-5 (Which is four times a number minus 5)
4n-6
1
14-4x6=
4x - 5
Four times greater.
3x-4