Final answer:
An inversely proportional relationship is best described by the phenomenon where pressure increases and volume decreases, in accordance with Boyle's Law, illustrating that pressure and volume are inversely related at a constant temperature.
Step-by-step explanation:
The statement that best describes an inversely proportional relationship is that pressure increases but volume decreases. This relationship is well captured by Boyle's Law, which states that at a constant temperature, pressure and volume are inversely proportional to each other. As a result, if we increase pressure, we observe that volume correspondingly decreases, and vice versa.
As seventeenth-century scientists discovered, if the temperature of the gas is held constant, and when the pressure on the gas is increased, the volume will decrease to maintain a constant number of moles of gas. Mathematically, this can be expressed as P⋅V = k, where P is pressure, V is volume, and k is a constant. Thus, the correct answer to our question is that when pressure increases but volume decreases, the relationship is one of inverse proportionality.