Which of the following variables is a measure of the average kinetic energy of the molecule of a gas?

Step 1: Analyze the question The question asks which variable measures the average kinetic energy of gas molecules.

Step 2: The concept According to the kinetic theory of gases, gas molecules are in constant, random motion. The average kinetic energy of these molecules is directly proportional to the absolute temperature (in kelvin):

where k is the Boltzmann constant and T is the temperature in kelvin.

Step 3: Check each option

• A. Density: This is mass per unit volume. It tells you how closely packed the molecules are, not how fast they move.
• B. Pressure: This results from molecular collisions with the container walls. It depends on both the number of molecules and their energy, and it also depends on volume, so it is not a direct measure of average kinetic energy.
• C. Temperature: Correct. Temperature is the measure of the average kinetic energy of the particles. When you heat a gas, its molecules move faster, and their average kinetic energy increases.
• D. Volume: This is the space the gas occupies. It is not a measure of molecular energy.

Step 4: Answer The correct option is **C.

Exam tip: Remember "Temperature = Total average motion energy". Whenever you see "average kinetic energy" in a question, think of temperature. This is also why, in Kelvin, doubling the temperature doubles the average kinetic energy.