Which of the following is not a postulate of the kinetic-molecular theory? a. gas particles have a high force of attraction to one another or to the walls of the container. b. the distance between gas particles is much larger than the size of the particles themselves. c. gas particles will always travel in a straight line until they hit a container wall or another gas particle. d. gases are made up of particles that act like little, hard spheres that are always moving in a random fashion.

Following are important postulates of Kinetic theory of gases

1) Gases are made up of number of particles. 
this particles  behaves like hard and spherical objects, which are in constant state of motion.
2)  The particles always travel in a straight line until they collide with another particle or the walls of the container.
3) Particles are of smaller size as compared to the distance between particles.
4) There exist minimal/no force of attraction between the gas particles neither there exist attractive interaction between the particles and the walls of the container.
5) Collisions between gas particles or with the walls of the container are  elastic in nature. 

Thus, statement a i.e. Gas particles have a high force of attraction to one another or to the walls of the container contradicts the postulates of kinetic theory of gases