The document discusses the arrangement of individual units in plastics, distinguishing between thermoplastics and thermosetting plastics. Thermoplastics are characterized by their ability to become liquid when heated and solidify into a glassy state when cooled. Conversely, thermosetting plastics undergo heavy cross-linking and do not remelt.

3. In Plastics, the arrangement of the individual
units may be linear or cross linked
Linear or lightly cross-linked polymers form
a class of plastics called thermoplastics
Heavy cross-linking plastics are called
thermosetting plastics

4. THERMOPLASTIC IS A POLYMER
THAT TURNS INTO A LIQUID
WHEN HEATED AND FREEZES
INTO A VERY GLASSY STATE
WHEN COOLED SUFFICIENTLY.