Which of the following has to remain constant to allow you to use the combined gas law for calculations?

Answer is amount or moles of gas.

Explanation:

Combined gas law is the law obtained by combination of the three gas laws for an ideal gas: Boyle's law,Charles's law and Gay-Lussac's law.

Boyle's law : pressure and volume of an ideal are inversely proportional. at constant temperature and moles.

Charles's law: Volume of a gas is directly proportional to temperature of gas, at constant pressure and moles.

Gay-Lussac's law: Pressure of a gas is directly proportional to temperature of gas, at constant volume and moles.

Combined gas law is PV/T = constant

So this is true for constant moles of gas or amount of gas.

answerspecific gravity;