Which one of the following is the wrong assumption of kinetic theory of gases ?

• A

  Momentum and energy always remain conserved.
• B

  Pressure is the result of elastic collision of molecules with the container's wall.
• C

  Molecules are separated by great distances compared to their sizes.
• Correct answer
  D

  All the molecules move in straight line between collision and with same velocity.

Hence, the correct answer is option: 'D'.