Answer: The correct answer is volume and temperature.
Explanation:
Charles' Law states that volume is directly proportional to the temperature of the gas at constant pressure and number of moles of gas.
Mathematically,
[tex]\text{Volume}\propto \text{Temperature}[/tex]
Or,
[tex]V\propto T[/tex] (At constant pressure and number of moles)
As, the temperature of the gas increases, volume of the gas also increases and vice-versa.
Hence, the correct answer is volume and temperature.