Assertion : Bharat stage IV emission norms have been in place since April 2010, for 4 wheelers in 13 mega cities of India.
Reason : Green muffler scheme refers to the plantation of trees and shrubns along road sides and is effective to control noise pollution only.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Assertion:**
- The assertion states that Bharat Stage IV emission norms have been in place since April 2010 for four-wheelers in 13 mega cities of India.
- This is true as the Bharat Stage emission standards are regulations set by the Government of India to control air pollution by setting limits on the amount of pollutants that can be emitted by vehicles.

2. **Identifying the 13 Mega Cities:**
- The 13 mega cities mentioned in the assertion include: Delhi, NCR, Mumbai, Kolkata, Chennai, Bangalore, Surat, Kanpur, Agra, Lucknow, and Varanasi (Cholapur is a typo; it should be Varanasi).
- These cities were targeted for stricter emission norms to combat severe air pollution.

3. **Understanding the Reason:**
- The reason provided states that the Green Muffler Scheme refers to the plantation of trees and shrubs along roadsides and is effective only in controlling noise pollution.
- This statement is incorrect because while the Green Muffler Scheme does help in reducing noise pollution, it also plays a significant role in reducing air pollution.

4. **Clarifying the Role of Green Muffler Scheme:**
- The Green Muffler Scheme involves planting trees and shrubs that act as natural barriers to absorb sound and filter air pollutants.
- Trees and shrubs can absorb harmful gases and particulate matter from the air, thus contributing to improved air quality.

5. **Conclusion:**
- The assertion is correct, while the reason is incorrect. Therefore, the correct relationship is that the assertion is true, but the reason does not accurately reflect the full impact of the Green Muffler Scheme.

**Final Answer:**
- Assertion: True
- Reason: False

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