Final answer:
The statement is true; the combined gas law relates pressure, temperature, and volume of a fixed amount of gas, and is used when all three properties change.
Step-by-step explanation:
The statement that the combined gas law states the relationship among pressure, temperature, and volume of a fixed amount of gas is true. The combined gas law is an amalgamation of several simpler gas laws, each of which describes two of the three variables (pressure, temperature, and volume) while holding the third constant. However, in situations where all three variables change, the combined gas law comes into play, providing a way to understand how these properties of a gas are interrelated.
The mathematical form of the combined gas law is often written as (P1V1/T1) = (P2V2/T2) where P represents pressure, V is volume, T is absolute temperature, and the subscripts 1 and 2 refer to the initial and final states of the gas, respectively. When using this formula, it's crucial to ensure that the temperature is measured in Kelvin to maintain the direct proportionality defined by Charles's Law, and pressure is consistent in its units.