Everything from the 2 lessons of this topic on a few pages: the key idea of each lesson, the diagram to remember, the points to learn and the traps examiners set. Read it, cover it, test yourself.
In a solid the particles are close together in a regular arrangement and vibrate about fixed positions, so a solid has a fixed shape and volume. In a liquid they are close together but irregular and move around each other, so a liquid has a fixed volume but takes the shape of its container. In a gas they are far apart, randomly arranged and move quickly in all directions, so a gas has no fixed shape or volume and is easily compressed. Heating gives particles more kinetic energy; changes of state happen when the forces between particles are overcome or formed.
A flat section on a heating curve does not mean the heating has stopped. Energy is still going in, but it is being used to overcome the forces between particles, so the kinetic energy and the temperature stay the same until the change of state is complete.
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, caused by their random motion. No stirring is needed. Diffusion is fast in gases, much slower in liquids, and faster at higher temperatures because the particles move faster. Extended: at the same temperature, particles with a lower relative molecular mass move faster, so a gas with a lower Mr diffuses faster.
The white ring forms closer to the hydrochloric acid end, not in the middle and not near the ammonia. Explain it with relative molecular mass and speed of particles: saying the ammonia is "stronger" or "more concentrated" earns no marks.