Derive the formula for a substance containing 85.7% carbon and 14.3% hydrogen.

Derive the formula for a substance containing 85.7% carbon and 14.3% hydrogen. The relative hydrogen vapor density of this substance is 14

Let’s designate the unknown substance as CxHy.
Let’s compose the ratio of the percentage to molar mass.
CxHy = 85.7 / 12: 14.3 / 1 = 7.14: 14.3.
Let’s round to the nearest whole number by dividing by the smallest value.
CxNy = 1: 2.
The molar mass of the resulting substance is Mr (CH2) = 14.
Let us find the true molar mass of a substance, knowing the vapor density of carbon.
Mr (CxHy) = D (H2) • Mr (H2) = 14 • 2 = 28.
Let’s set the coefficients according to the formula.
CxHy = Mr (source) / Mr (CH2) = 28/14.
Hence the formula of the substance C2H4 is ethylene.