Question

Assertion: Ozone is getting depleted due to $\mathrm{CFCs}$.

Reason: With the depletion of the ozone layer more UV radiation filters into the troposphere.

• A. Both assertion and reason are true and reason is the correct explanation of the assertion.
• B. Both assertion and reason are true and reason is not the correct explanation of the assertion.
• C. Assertion is true but reason is false.
• D. Assertion is false but reason is true.

Answer 1

The correct option is B

Both assertion and reason are true and reason is not the correct explanation of the assertion.

1. The presence of ozone $\left({\mathrm{O}}_3\right)$ in high concentration in the stratosphere region of the atmosphere is known as the ozone layer. It protects the earth from the harmful ultraviolet radiations of the sun as it acts as a barrier for UV radiation and does not let them enter inside the earth's atmosphere ( in the troposphere region- lowest region of the atmosphere).
2. But the concentration of ozone is depleting in the stratosphere which is termed as ozone layer depletion. Some chemical compounds are responsible for this depletion as they react with ozone in the stratosphere region thereby decreasing its concentration. They are known as ozone-depleting compounds. For example- chlorofluorocarbons $\left(\mathrm{CFCs}\right)$, hydrochlorofluorocarbon $\left(\mathrm{HCFCs}\right)$, carbon tetrachloride $\left({\mathrm{CCl}}_4\right)$, chloromethane $\left({\mathrm{CH}}_3\mathrm{Cl}\right)$ etc. These compounds release bromine and chlorine which reacts with ozone.
3. The reaction is given below -

. $$\begin{gathered} 1.\underset{\left(\mathrm{Chloromethane}\right)}{{\mathrm{CH}}_3\mathrm{Cl}}\stackrel{\mathrm{UV}\mathrm{radiation}}{\to }\mathrm{Cl}·+·{\mathrm{CH}}_3 \\ 2.\mathrm{Cl}·+{\mathrm{O}}_3\to \mathrm{ClO}+{\mathrm{O}}_2 \\ 3.\mathrm{ClO}+{\mathrm{O}}_3\to \mathrm{Cl}·+2{\mathrm{O}}_2 \end{gathered}$$

4. Ozone is getting depleted due to $\mathrm{CFCs}$. With the depletion of the ozone layer more UV radiations filters into the troposphere (the lowest region of the atmosphere). Both the assertion and reason are true but the reason given here is the effect of assertion and not its reason.

So, both the assertion and reason are true and the reason is not the correct explanation of the assertion.

Hence, option B is the correct answer.