The combustion reaction of acetylene has a balanced equation like so:
C2H2 + 3O2 --> 2H2O + 2CO2
Using the ratio 1:3:2:2, if 1.10 mols of CO2 are produced, assuming complete combustion, than that means that 0.55 mols of acetylene (C2H2) must have been combusted. The molar mass of acetylene is 26, so the answer is 26*0.55 = 14.3 grams
