Brownian motion can be observed when looking at tiny pollen grains suspended in water under a microscope.
What causes the pollen grains to move in a random, jerky fashion?
The pollen grains are colliding with fast-moving, invisible water molecules.
Convection currents within the water carry the pollen grains.
The pollen grains are alive and swimming in the water.
Mutual gravitational attraction between the pollen grains.
321 exam-style questions on CIE IGCSE Physics 2.1 Kinetic particle model of matter, covering 2.1.1 States of matter and changes of state, 2.1.2a Particle structure and motion in solids, liquids and gases, 2.1.2b Gas pressure and particle collisions, 2.1.2c Brownian motion, 2.1.3a The absolute scale of temperature, and 2.1.3b Pressure, volume and temperature of a gas. Each one has a worked solution and a mark scheme showing where the marks go.