Answer:
A. Gas particles are in constant motion.
Step-by-step explanation:
The first postulate of Kinetic Molecular Theory is that gas particles are in constant motion.
B is wrong. Kinetic Molecular Theory assumes that there are no attractive forces between the molecules.
C is wrong. Kinetic Molecular Theory assumes that collisions between molecules are elastic.
D is wrong. Kinetic Molecular Theory assumes that there are no attractive forces between the molecules of the gas and those of its container.
