In the ideal gas law PV = nRT, what is true about temperature?

• A. Temperature must be in Kelvin
• B. Temperature must be in Celsius
• C. Temperature must be in Fahrenheit
• D. Temperature is dimensionless

Answer: (A)

In the ideal gas law, temperature represents an absolute thermodynamic temperature. Kelvin is used because it starts at absolute zero and increases in equal steps that correspond directly to changes in the molecules’ average kinetic energy. This makes PV proportional to T for a fixed amount of gas and volume, so the gas constant R connects those quantities with consistent units.

If you used Celsius or Fahrenheit directly, you’d be introducing offsets (since those scales have nonzero values at 0 °C or 0 °F), which would spoil the simple proportional relationship unless you first convert to Kelvin. The standard form of the equation assumes T is in kelvin, and R is defined with those units. Temperature in this context is not dimensionless; Kelvin provides the proper, universal scale for the equation to hold.