Which is not an assumption about particles in a gas according to the kinetic theory? the motion of one particle is unaffected by other particles unless the particles collide. the forces of attraction among particles keep the particles close together. under ordinary conditions, forces of attraction between particles can be ignored.

Let us evaluate the given assumptions according to the kinetic theory for an ideal gas.

a.
The motion of one particle is unaffected by other particles unless the particles collide.
TRUE. The particles are in random motion unless they collide.

b.
The forces of attraction among particles keep the particles close together.
FALSE. No forces act between particles except during collision.

c.
Under ordinary conditions, forces of attraction between particles can be ignored.
TRUE. 

Statement b is false because it is not an assumption.