JEE Advanced levelSingle correct optionDifficulty 3 of 3pl144
Assertion (A): Natural rubber is elastic, whereas gutta-percha, which has the same constitution (1,4-polyisoprene), is hard and non-elastic.
Reason (R): The cis double bonds of natural rubber give coiled chains that pack poorly with weak interchain forces, whereas the trans double bonds of gutta-percha let chains pack regularly with stronger interchain forces.
ABoth A and R are true and R is the correct explanation of A
BBoth A and R are true but R is not the correct explanation of A
CA is true but R is false
DA is false but R is true
Answer: A
Both statements are true. The cis geometry prevents close packing, so chains can stretch and recoil; the trans geometry allows regular packing and stronger forces, which makes the material rigid. R therefore explains A.