Pollen grains suspended in water are observed under a microscope to move in a random, zigzag motion. Which statement explains why the pollen grains move in this way?
They are hit by water molecules.
They are alive and swimming.
They are moved by convection currents in the water.
They are repelled by the light.
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.