Which gas law involves the relationship of combining volumes of gases expressed in small whole numbers?

The correct choice pertains to Avogadro's Law, which specifically addresses the relationship between the volume of gas and the amount (in moles) of gas at a fixed temperature and pressure. Avogadro's Law states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules. This law emphasizes the direct proportionality between the volume of a gas and the number of moles of gas, indicating that when gases react together, they do so in volumes that are simple whole-number ratios.

This concept is significant in stoichiometry and in understanding gas reactions, as it helps predict the volumes of gases produced or consumed in a chemical reaction. The application of this law illustrates how gases combine in predictable, quantifiable ways, aligning with the small whole numbers observed in gas reactions.

The other options pertain to different relationships: Boyle's Law relates pressure and volume at constant temperature, Charles' Law connects volume and temperature at constant pressure, while Gay-Lussac's Law deals with pressure and temperature at constant volume. Each of these laws describes different aspects of gas behavior, but they do not specifically address the combining volumes of gases in whole number ratios like Avogadro's Law does.