Final answer:
Ideal gas particles move randomly, which is a fundamental aspect of the kinetic-molecular theory of gases. They have kinetic energy that is dependent on the temperature, and they exert no attractive or repulsive forces on one another. Gas particles do have mass, contrary to the incorrect options provided.
Step-by-step explanation:
The ideal gas particles: a) move randomly. This fact is a fundamental characteristic described by the kinetic-molecular theory of gases, which indicates that gas particles are in constant, random motion. Thus, option a is the correct completion for the statement. In contrast, option b) have no kinetic energy is incorrect because the average kinetic energy of gas particles is proportional to the Kelvin temperature of the gas. Option c) repel each other at high pressure is not accurate in the context of an ideal gas, for ideal gas particles exert no attractive or repulsive forces on each other. Lastly, option d) have no mass is incorrect because gas particles do indeed have mass, even though they are very small.