Evaluating Assertion (A): Upper Atmosphere Shields Life

The assertion states that the upper atmosphere shields life on Earth. This is factually correct. The Earth's atmosphere, particularly layers like the stratosphere containing the ozone layer, acts as a protective barrier against harmful solar radiation.

Evaluating Reason (R): UV Radiation Absorption

The reason given is that ultraviolet (UV) radiations are absorbed in the upper atmosphere. This statement is also factually correct. The ozone layer ($O_3$) within the stratosphere absorbs the majority of the Sun's harmful ultraviolet radiation, preventing it from reaching the Earth's surface.

Analyzing the Relationship Between Assertion and Reason

While the absorption of UV radiation (Reason R) is a crucial part of how the upper atmosphere shields life (Assertion A), it might not be considered the sole or complete explanation. The upper atmosphere provides shielding through various mechanisms, including:

• Absorption of harmful UV radiation by the ozone layer.
• Absorption of other high-energy radiation (like X-rays and gamma rays) in the thermosphere and ionosphere.
• Protection from meteoroids burning up upon entry.
• Regulation of temperature.

Therefore, although Reason (R) is true and directly contributes to Assertion (A), it doesn't encompass the entirety of the shielding effect provided by the upper atmosphere. Hence, (R) is not the complete or sole correct explanation for (A).

Determining the Correct Option

Based on the analysis:

• Assertion (A) is true.
• Reason (R) is true.
• Reason (R) is not the sole or complete explanation for Assertion (A).

This corresponds to Option 2.