mol ratio

an organic compound was found to consist of carbon and hydrogen only
0.781g of the compound was burnt, 2.64g of CO2 and 0.54g of H2O were formed
relative molecular mass was approximately 78

The empirical formula is CxHy

CxHy ---> xCO2 + y/2 H2O on complete combustion

molar mass of C is 12g
molar mass of H is 1g
molar mass of CO2 is 44g
molar mass of H2O is 18g

number of mole of CO2 s 2.64/44 = 0.06
number of mole of H2O s 0.54/18 = 0.03
so x = 0.06 y = 2(0.03) = 0.06
x : y = 1:1
x = y in the formula CxHy => CxHx

molar mass of CxHy = 12 * x + 1 * x
= 13x = 78
x = 5

The empirical formula is C5H5

I hope this can help your understanding. =)

The molecular formula of the compound is CxHy