Statement I : The order of extent of attractive forces between monomers is fibres > thermoplastic polymers > elastomers
Statement II : Thermoplastic polymers become soft on heating
Statement III : Thermosetting polymers become hard on heating
Correct statement is / are

The correct statements are:

Statement I: The order of extent of attractive forces between monomers is fibres > thermoplastic polymers > elastomers.

This statement is generally true. Fibers, such as those found in silk or wool, are held together by strong intermolecular forces, such as hydrogen bonding. Thermoplastic polymers, such as polyethylene or polystyrene, are held together by weaker intermolecular forces, such as Van der Waals forces, which allow them to soften and melt upon heating. Elastomers, such as rubber, are held together by even weaker forces, which allow them to stretch and return to their original shape.

Statement II: Thermoplastic polymers become soft on heating.

This statement is true. Thermoplastic polymers are capable of softening and melting upon heating due to their relatively weak intermolecular forces. This property allows them to be easily molded or shaped into various forms.

Statement III: Thermosetting polymers become hard on heating.

This statement is also true. Thermosetting polymers, unlike thermoplastic polymers, do not soften upon heating. Instead, they undergo a permanent chemical change upon heating, known as curing or crosslinking, which forms strong covalent bonds between the polymer chains. This crosslinking makes the polymer network more rigid and less susceptible to deformation, resulting in a hard and inflexible material. Examples of thermosetting polymers include epoxy resins and phenolic resins.