To find the molar mass of CxHy, we first need to determine the molar mass of CO2 $carbondioxide$ and H2O $water$.

Calculate the molar mass of CO2:

Carbon $C$: 1 atom x 12.01 g/mol = 12.01 g/molOxygen $O$: 2 atoms x 16 g/mol = 32 g/mol
Molar mass of CO2 = 12.01 + 32 = 44.01 g/mol

Calculate the molar mass of H2O:

Hydrogen $H$: 2 atoms x 1.01 g/mol = 2.02 g/molOxygen $O$: 1 atom x 16 g/mol = 16 g/mol
Molar mass of H2O = 2.02 + 16 = 18.02 g/mol

Now, use the given information to find the number of moles of CxHy:

Volume of CxHy = 1 molVolume of CO2 = 67.2 LVolume of H2O = 72 g $assumeatstandardconditions$ Since 1 mol of any gas occupies 22.4 L at STP, the volume in liters of CO2 and H2O can be converted to moles using their molar volumes:
Moles of CO2 = 67.2 L / 22.4 L/mol = 3 moles
Moles of H2O = 72 g / 18.02 g/mol = 3.99 moles

Given that the reaction for the combustion of CxHy produces CO2 and H2O, we can determine the molar ratio of CxHy to CO2 and H2O using the coefficients in the balanced chemical equation. Since the number of moles of CO2 and H2O is equal, the molar ratio of CxHy to the products is 1:3. Therefore, 1 mole of CxHy produces 3 moles of CO2 and H2O.

Since the volume of CO2 is 3 moles and the molar mass of CO2 is known, we can calculate the moles of carbon in CO2:
Moles of carbon in CO2 = 3 moles x 12.01 g/mol = 36.03 g of carbon

Given that each mole of CxHy contains x moles of carbon, we can equate it to the moles of carbon in the reaction:
x = 36.03 g / molar mass of CxHy

The molar mass of CxHy can now be calculated as:
molar mass of CxHy = 36.03 g / x

Now, we know that the molar mass of CxHy is 36.03 g divided by a whole number x. Thus, the molar mass of CxHy is likely to be around 36 g/mol.