C. the relative number of atoms of each element, using the lowest whole ratio.
Explanation:
The empirical formula is how we simplify the whole formula to simplify it to its smallest indivisible parts.
It is definitely not the actual number of atoms. If you see an empirical formula, don't think that it's the full thing.
It is also not a representation of a compound to show its atoms' arrangement: this would be a Lewis dot structure, or a ball and stick model, or something similar. We don't use the empirical formula for this purpose.
