JEE Main levelSingle correct optionDifficulty 2 of 3pl082
Assertion (A): Raw natural rubber is soft and sticky and becomes brittle in cold weather. Reason (R): Its linear cis-polyisoprene chains are held only by weak van der Waals forces and can slide past one another.
ABoth A and R are true but R is not the correct explanation of A.
BBoth A and R are true and R is the correct explanation of A.
CA is true but R is false.
DA is false but R is true.
Answer: B
Without cross-links, chains of raw rubber move over one another and the material deforms permanently or flows when warm. Vulcanisation introduces covalent bridges to cure this behaviour. So R explains A.