The rapid movement of gas molecules can be explained because gasses have small size particles and exert little attraction for other gas particles.
Explanation
The particles present in the gas are loosely packed and can move freely inside when compared to the particles present in both liquid and solid state.
Therefore, gas particles have high inter-molecular space.
Also, as these gas particles are loosely packed, the force of attraction between each molecule is less.
To sum up, the particles present have high inter-molecular space and low inter-molecular force of attraction.