Which of the following is a cross-linked polymer?

Which of the following statements is correct regarding the drawbacks of raw rubber?

Given below are two statements,one is Assertion $(A)$ and the other is Reason $(R).$
Assertion $(A):$ Natural rubber is a linear polymer of isoprene called cis-polyisoprene with elastic properties.
Reason $(R):$ The cis-polyisoprene molecules consist of various chains held together by strong polar interactions with a coiled structure.
In the light of the above statements,choose the correct one from the options given below:

Which of the following has been used in the manufacture of non-inflammable photographic films?

Which of the following processes develops cross-links in elastomer?

Buna-$S$ is obtained from