Change of state

I don't understand why this is highlighted bold in the specification, showing that it's for Single Science, because this is so simple. 

5.7 understand that a substance can change state from solid to liquid by the process  of melting

5.8 understand that a substance can change state from liquid to gas by the process of evaporation or boiling

5.9 recall that particles in a liquid have a random motion within a close-packed irregular structure

5.10 recall that particles in a solid vibrate about fixed positions within a close-packed regular structure

State of matter	Arrangement of particles	Movement of particles
Solid	Closely packed together, usually in a regular pattern, occupying minimum space. This results in solids having high densities.	Vibrate about fixed positions only. Held in position by very strong intermolecular bonds. This explains why solids have fixed volumes and shapes.
Liquid	Randomly arranged with the particles slightly further apart as compared to that of solids. This results in liquids having  relatively high densities.	Free to move about but confined within the vessel containing it. Have attractive forces between particles. This explains why liquids have fixed volume but will take the shape of vessels containing them.
Gas	Very far apart. Particles are randomly arranged and will occupy any available space. This results in gases having very low densities.	Particles have very little attraction between them and move about randomly at very high speed. This explains why gases have no fixed volume and shape, and why they are highly compressible.