Assertion : If earth did not have atmosphere, its average surface temperature would be lower than what it is now
Reason : Green house effect of the atmosphere would be absent, if earth did not have atomosphere.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false

Explanation

To solve the question, we need to analyze the assertion and the reason provided:

**Assertion:** If Earth did not have an atmosphere, its average surface temperature would be lower than what it is now.

**Reason:** The greenhouse effect of the atmosphere would be absent if Earth did not have an atmosphere.

### Step-by-Step Solution:

1. **Understanding the Assertion:**
- The assertion states that without an atmosphere, the average surface temperature of the Earth would be lower than it is currently. This is a true statement. The atmosphere plays a crucial role in regulating the Earth's temperature.

**Hint:** Consider how the atmosphere influences temperature retention on Earth.

2. **Understanding the Reason:**
- The reason given is that the greenhouse effect would be absent without an atmosphere. This is also true. The greenhouse effect is primarily caused by gases in the atmosphere (like carbon dioxide, methane, etc.) that trap heat.

**Hint:** Think about what the greenhouse effect does and which gases are responsible for it.

3. **Connecting the Assertion and Reason:**
- The assertion and reason are connected. The greenhouse effect is responsible for keeping the Earth's surface warm by trapping heat. Without the atmosphere, there would be no greenhouse gases to retain heat, leading to lower average temperatures.

**Hint:** Reflect on how the absence of the greenhouse effect directly relates to temperature changes.

4. **Conclusion:**
- Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the correct answer is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.

**Hint:** Review the definitions of assertion and reason to ensure clarity in your conclusion.

### Final Answer:
Both the assertion and reason are true, and the reason is the correct explanation for the assertion.