An unidentified gas is determined to be 24.0% carbon and 76% fluorine by mass. What is the empirical formula of this gas

CF₂

Explanation:

Let's assume we have 100 g of the gas. If that were the case we'd have

Now we convert both masses into moles, using their respective molar mass:

We can express those results as C₂F₄.

To determine the empirical formula we reduce those coefficients to the lowest possible integers, leaving us with CF₂.