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In a mixture of argon and nitrogen gases at room temperature, consider a single collision between one argon molecule and one nitrogen molecule. Which of the following outcomes are physically possible?

1. The kinetic energies of both molecules decrease after the collision.
2. The kinetic energies of both molecules increase after the collision.
3. The kinetic energy of the argon molecule increases and that of the nitrogen molecule decreases.
4. The kinetic energy of the nitrogen molecule increases and that of the argon molecule decreases.

Correct answer: The kinetic energy of the argon molecule increases and that of the nitrogen molecule decreases.

Solution

Kinetic energy is conserved overall in elastic collisions, so the total cannot increase or decrease — ruling out options A and B. Either C or D is possible depending on which molecule is faster before the collision. Both C and D are individually possible outcomes.

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