The mass fraction of carbon in the hydrocarbon is 83.3%. The relative density of the vapors of this substance

The mass fraction of carbon in the hydrocarbon is 83.3%. The relative density of the vapors of this substance in terms of hydrogen is 36. What is the molecular formula of the hydrocarbon.

If the density for H2 is 36, then the molecular weight is 36 * 2 = 72 amu, hence the mass of carbon atoms
equals: (72 * 83.3%: 100%) = 72 * 0.833 = 60 amu, and the number is 60: 12 = 5.
Since the atomic mass of hydrogen is 1 amu, then the mass and amount of hydrogen in the desired molecule: 72 * (1 –
0.833) = 72 * 0.167 = 12.
The hydrocarbon formula is C5H12, it is also pentane.