Of the following,which one is classified as a polyester polymer?

Buna-$S$ is a polymer of

Assertion: Rayon is a semi-synthetic polymer whose properties are better than natural cotton.
Reason: Mechanical and aesthetic properties of cellulose can be improved by acetylation.

Which one of the following polymers will not catch fire?

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 is used to make rubber hard for tire manufacturing?