C₂H₂ has  the greatest percent by mass of carbon (92.3%)
Further explanation
Given
Hydrocarbons
Required
The greatest percent by mass of Carbon
Solution
Proust states the Comparative Law that compounds are formed from elements with the same Mass Comparison so that compounds have a constant composition of elements
% A in AxBy = (x.Ar A/MW AxBy) x 100%
C₃H₄ = 3.12/40 x 100%=90%
CHâ‚„ = 12/16 x 100% = 75%
Câ‚‚Hâ‚„=2.12/28 x 100% = 85.7%
Câ‚‚Hâ‚‚=2.12/26 x 100% = 92.3%
