Are the particles in a solid motionless ?

No. Just because it is a solid doesn't mean it has no motion. The only way for particles to be motionless is for the solid to reach Absolute Zero (0* K). Which is impossible. So, therefore, it is impossible for particles in a solid to be motionless.

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.

Answer(28.02g/mol);