Concept:Brownian motion is the erratic movement of microscopic particles in a fluid due to molecular collisions.Explanation:I is correct: Brownian motion is a rapid, constant, and irregular motion of tiny particles.II is correct: It provides evidence for the existence of molecules.III is incorrect: Brownian motion occurs in liquids and gases, not only in gases.IV is correct: It shows that molecules are in constant random motion.Answer:D. I, II and IV only