The substance that is added to make natural rubber strong and more bouncy is A. Polythene B. Sponge C. Sulphur D. Chlorine

The correct answer is C. Sulphur.

Sulphur is added to natural rubber to make it strong and more bouncy. This process is called vulcanization. When sulphur is added to rubber, it forms cross-links between the long chains of rubber molecules. This makes the rubber stronger and more elastic.

Polythene is a type of plastic. It is not added to natural rubber to make it strong and more bouncy.

Sponge is a type of material that is made from a network of small holes. It is not added to natural rubber to make it strong and more bouncy.

Chlorine is a type of element. It is not added to natural rubber to make it strong and more bouncy.