Question
Answers

The gas that develops cracks in rubber is:
[A] ${{O}_{2}}$
[B] ${{O}_{3}}$
[C] $C{{O}_{2}}$
[D] $S{{O}_{2}}$

Answer
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Hint: We know that rubber is a polymeric chain of different hydrocarbons. Attack of a certain gas affects the circumference of the material and causes it to crack. Chemically, the gas affects the double bonds of the material by cleaving it by formation of ozonide.

Complete answer:
Before answering this, let us discuss what rubber is and its types.
We should know that rubber is an elastic substance and it can be obtained naturally as well as synthetically.
The rubber that we obtain from certain tropical plants is known as natural rubber. We can also manufacture rubber from natural gas and petroleum and other derived hydrocarbons. This is known as synthetic rubber.
Natural rubber has high tensile strength and higher tear resistance compared to synthetic rubber but vulcanization of synthetic rubber makes it stronger.
Now, let us discuss the given question.
We know that rubber changes its properties when exposed to changing environment conditions.
In the elastomers like natural rubber, styrene – butadiene rubber etc. we often notice certain cracks in the surface. These cracks are formed due to ozone attacking the double bonds of the polymer chain and undergoing ozonolysis. It forms cracks at right angles to the strain axis and thus affect the circumference of the material.
Now let us discuss the process of ozonolysis-
Ozonolysis is the process of cleaving the double bond by the formation of a five membered ring. The formation of ozonide results in cleaving of the double bond and thus breaking of the double bond to give two separated products. We can show the reaction as-
\[{{R}_{1}}{{R}_{2}}C=C{{R}_{3}}{{R}_{4}}\xrightarrow{{{O}_{3}}}{{R}_{1}}{{R}_{2}}CO+{{R}_{3}}{{R}_{4}}CO\]
Here, the alkyl groups are denoted by R.
We can understand from the above discussion that crack in rubber is formed due to the action of ozone.

Therefore, the correct answer is option [B] ${{O}_{3}}$ .

Note:
Although 60% of the rubber industry is based upon synthetic rubber, the remaining 40% is still taken by natural rubber. Natural rubber is used in high performance racing tires and also for aircrafts and buses due to its strength. However, it does not perform well outdoors due to its lack of resistance towards heat aging caused by sunlight and also ozone cracking.