What is matter made of? ... Why is gravity so weird? ... Why does time seem to flow only in one direction? ... Where did all the antimatter go? ... What happens in the gray zone between solid and liquid? ... Can we find a unified theory of physics? ... How did life evolve from nonliving matter?

Dear student 

This is based on ideal gas law PV=nRT.
Where P is pressure, V is volume, R is gas constant and T is temperature. Hence from liquid to solid or solid to liquid the transition has to cross the grey zone.
This grey zone transition is is very crucial which includes the inter molecular forces acting on the molecules and each atoms which makes the change in state from hot to cold and cold to hot.
The best example is ice crystal formation and water formation from ice crystal .
Hence the inter molecular force of attraction happens to be involved with changes in grey zone.