Advanced Placement (AP) Chemistry Practice Exam

An empirical formula is specifically defined as the simplest whole-number ratio of the elements present in a compound. It reflects the relative proportions of each element but does not provide information about the actual number of atoms in a molecule or the structure of the compound. For example, the empirical formula for glucose (C₆H₁₂O₆) is CH₂O, which shows that the elements carbon, hydrogen, and oxygen are present in a 1:2:1 ratio.

In contrast, a molecular formula provides the actual number of atoms of each element in a molecule. This means that while the empirical formula gives a simplified view of the composition, the molecular formula gives a complete picture of the molecular structure.

The other options do not accurately capture the distinction between empirical and molecular formulas. For instance, indicating the actual number of atoms relates specifically to molecular formulas, and the concept of ratios does not pertain exclusively to mixtures but rather to the ratio of elements in a single compound. Moreover, empirical formulas can apply to compounds in various states, not just gases.