Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): The temperature increases in the troposphere from ground to tropopause.
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:

In the troposphere, temperature decreases with height (lapse rate).
In the stratosphere, temperature increases with height (thermal inversion) due to UV absorption by the ozone layer.
Remembering this alternating pattern helps solve atmospheric profile questions quickly.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The Earth's atmosphere is divided into distinct thermal layers (troposphere, stratosphere, mesosphere, and thermosphere) based on how temperature changes with altitude.
This vertical temperature gradient is governed by the primary heat absorption mechanisms in each layer.

Step 2: Detailed Explanation:
Let us analyze the Assertion and Reason statements separately:
- Assertion (A): The troposphere is the lowest layer of the atmosphere, extending from the Earth's surface up to the tropopause (approximately 8 to 18 km altitude).
The troposphere is primarily heated from below by the Earth's surface, which absorbs solar radiation and re-radiates it as long-wave thermal energy.
Consequently, the temperature in the troposphere decreases with altitude at an average rate of \(6.5^{\circ}\text{C}\) per kilometer, known as the normal lapse rate.
The temperature reaches its minimum at the tropopause.
Therefore, the statement that temperature increases in the troposphere from the ground to the tropopause is incorrect.
- Reason (R): The stratosphere lies directly above the tropopause.
This layer contains a high concentration of ozone (\(\text{O}_3\)) molecules, which absorb harmful, high-energy ultraviolet (UV) radiation from the sun.
This exothermic chemical reaction releases heat energy, causing the temperature in the stratosphere to increase with altitude.
Therefore, the reason statement is correct.
Since the Assertion is false and the Reason is true, option (D) is the correct choice.

Step 2: Final Answer:
Assertion (A) is false but Reason (R) is true.