Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: The temperature increases with increasing height in the stratosphere.
Reason R: Ozone absorbs ultra violet radiation in the stratosphere and makes it warm.
In light of the above statements, choose the correct answer from the options given below:

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is NOT the correct explanation of A
• C. A is true but R is false
• D. A is false but R is true

Hint:

Remember the temperature behaviors in atmospheric layers:
- Troposphere: Temperature decreases with height (normal lapse rate).
- Stratosphere: Temperature increases with height (due to ozone UV absorption).
- Mesosphere: Temperature decreases with height.
- Thermosphere: Temperature increases with height (due to solar X-ray absorption).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The Earth's atmosphere is divided into several layers based on temperature gradients.
In the troposphere, temperature decreases with height.
However, in the stratosphere, this trend is reversed due to the presence of specific chemical species that interact with solar radiation.

Step 2: Detailed Explanation:
Let us analyze both the Assertion and the Reason:
- Assertion A: The stratosphere is the second major layer of the atmosphere, extending from approximately \( 10 \text{ km} \) to \( 50 \text{ km} \) above the Earth's surface.
Unlike the troposphere, the temperature in the stratosphere increases with altitude, rising from about \( -56^\circ\text{C} \) at the tropopause to near \( 0^\circ\text{C} \) at the stratopause.
Therefore, Assertion A is true.
- Reason R: The stratosphere contains a high concentration of ozone (\( \text{O}_3 \)) molecules, forming the ozone layer.
These ozone molecules are highly effective at absorbing harmful ultraviolet (UV-B and UV-C) radiation emitted by the sun.
The absorption of this high-energy radiation triggers photochemical reactions that release thermal energy, directly heating the surrounding air.
Since the upper parts of the stratosphere receive the highest intensity of unfiltered solar UV radiation, the heating is most intense at the top of this layer.
This direct absorption of UV radiation by ozone explains why the temperature rises with increasing height in this region.
Therefore, Reason R is true and provides the correct scientific explanation for Assertion A.

Step 3: Final Answer:
Both A and R are true and R is the correct explanation of A.