The correct answer is option 'C': The average kinetic energy of a molecule in an ideal gas is proportional to the absolute temperature of the gas.

Explanation:
In order to understand why the average kinetic energy of a molecule in an ideal gas is proportional to the absolute temperature of the gas, let's break it down into smaller components:

1. Kinetic Energy:
- Kinetic energy refers to the energy possessed by an object due to its motion.
- In the context of gases, the kinetic energy of individual gas molecules is directly related to their velocity. Higher velocity implies higher kinetic energy.

2. Ideal Gas:
- An ideal gas is a theoretical concept that assumes certain idealized conditions, such as negligible intermolecular forces and the absence of volume occupied by the gas molecules.
- In an ideal gas, the only force acting on the gas molecules is due to collisions with the walls of the container.

3. Kinetic Theory of Gases:
- The kinetic theory of gases describes the behavior of gases based on the motion of individual gas molecules.
- According to this theory, gas molecules are in constant random motion, colliding with each other and the walls of the container.
- The average kinetic energy of a gas molecule is directly related to its temperature.

4. Relationship between Kinetic Energy and Temperature:
- The kinetic energy of a gas molecule is directly proportional to its temperature.
- As the temperature of a gas increases, the average kinetic energy of the gas molecules also increases.
- This is because an increase in temperature implies an increase in the average velocity of the gas molecules.
- The relationship between kinetic energy and temperature is given by the equation: K.E. = (3/2) kT, where K.E. is the kinetic energy, k is the Boltzmann constant, and T is the absolute temperature.

Based on these principles, we can conclude that the average kinetic energy of a molecule in an ideal gas is proportional to the absolute temperature of the gas.