Final answer:
Inversely proportional means as one quantity increases, the other decreases; directly proportional means as one quantity increases, the other increases. Boyle's Law is an example of inverse proportionality, relating pressure and volume. Avogadro's Law is an example of direct proportionality, relating the number of molecules and volume.
Step-by-step explanation:
Inversely proportional means that as one quantity increases, the other quantity decreases, and vice versa. For example, Boyle's Law states that for an ideal gas, the pressure and volume are inversely proportional. As the volume of a gas increases, the pressure decreases, and as the volume decreases, the pressure increases.
The "other things" that must be equal in Boyle's Law are the temperature and the amount of gas. The law assumes that the temperature remains constant and that the amount of gas does not change.
On the other hand, directly proportional means that as one quantity increases, the other quantity increases as well, and as one quantity decreases, the other quantity decreases too. For example, Avogadro's Law states that the number of molecules in a gas is directly proportional to the volume of the gas. If the volume of a gas doubles, the number of molecules also doubles, and if the volume halves, the number of molecules also halves.
The "other things" that must be equal in Avogadro's Law are the pressure and temperature. The law assumes that the pressure remains constant and that the temperature does not change.