JEE Main 2022 · 29 June · morning · Single correct · +4 / −1
The polymer, which can be stretched and remains its original status on releasing the force is
- (a) Bakelite.
- (b) Nylon 6, 6.
- (c) Buna-N.
- (d) Terylene.
Answer and solution
Answer (c) Buna-N.
Solution
Chemistry ma’am · 3 steps
Stretch it, let go, and it snaps back: that is an elastomer, and Buna-N is the only rubber here.
- What the property means. A polymer that stretches under force and returns to its shape when released is an elastomer. Its chains are held by the weakest intermolecular forces, so they can uncoil and recoil.
- Why it springs back. A few cross-links tie the coiled chains together. When the force is removed, these cross-links pull the chains back to their original positions.
Polymer Class by intermolecular forces Behaviour Bakelite Thermosetting polymer Rigid, heavily cross-linked, does not stretch Nylon 6,6 Fibre Strong hydrogen bonds, high tensile strength Buna-N Elastomer Stretches and returns to shape Terylene Fibre Strong dipole forces, chains packed tightly - So. Buna-N, a synthetic rubber made from CH₂=CH-CH=CH₂ and acrylonitrile, is the elastomer. The answer is (c).
The idea to keep. Weakest forces with a few cross-links give elastomers (Buna-S, Buna-N, neoprene). Strong hydrogen bonds or dipole forces give fibres. A dense 3D network gives thermosets.
Answer from the NTA final answer key. Solution by PrepWiser.