While chlorofluorocarbons (CFC) are compounds that seem incredibly useful in industry, they also seem to wreak havoc on the ozone layer

In chemistry, you can never compare the masses of two different compounds, nor two different elements in a quantitative manner, you must compare them on a mole to mole basis.

In these types of questions, you need to take an imaginary 100 grams of the compound.

In that 100 gram sample, you will hace 80.46 grams of chlorine, 10.90 grams of carbon and the remainder (8.64 grams) of fluorine.

We have a mass relation, but we need a mole relation.

We need to know their relative abundances on a molar ratio.... take each mass, and convert them into a number of moles.

For instance we take our 80.46 grams of chlorine and divide that mass by the molar mass (found on the periodic table) of chlorine.

We should find that we have 2.27 moles of Cl...

Following the same procedure for Carbon and fluorine we should end up with 0.91 moles of carbon, and 0.455 moles of fluorine.

We need to convert these decimals into whole number ratios.... the best way is to divide all the values by the smallest value.

2.27/0.45 = 4.98 ~ 5
0.91/0.45 = 2
0.455/0.455 = 1

and this is the empirical formula C2Cl5F