How does the volume of a gas relate to the number of molecules at constant temperature and pressure?

The relationship between the volume of a gas and the number of molecules at constant temperature and pressure is described by Avogadro's Law, which states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules. Therefore, when the number of gas molecules increases, the volume occupied by the gas also increases, provided the temperature and pressure remain constant. This directly proportional relationship indicates that if you double the number of molecules of a gas, the volume will also double.

In contrast, other options suggest different relationships that do not hold true under the conditions specified (constant temperature and pressure). For instance, an inverse relationship would imply that increasing the number of molecules would lead to a decrease in volume, which contradicts Avogadro's principle. Additionally, saying the volume is constant or unrelated to the number of molecules fails to account for the fundamental behavior of gases outlined in the gas laws. Thus, the correct answer illustrates the foundational principle in gas behavior, confirming the direct proportionality between volume and the number of gas molecules under the specified conditions.