Suppose the volume is 1L, then the mass is 1.17g, 1/22.4=0.0446 mol, 1.17/0.0466=26, 26/(12+1)=2, so its molecular formula is C2H2.
The density of acetylene at STP is 1.17g/L. The empirical formula of acetylene is CH. Describe how you can determine the molar mass of acetylene and its molecular formula if you know only its density at STP and its density?