Assertion : An equilibrium is established is istablished between generation and destruction of ozone, leading to a steady state concentration of ozone layer in the stratosphere at an altitude of 20-30 km above sea level.
Reason : The thickness of the ozone layer is generally larger above the equator and smaller above the poles.

Answer

To analyze the assertion and reason provided in the question, we will break down the concepts step by step.

### Step 1: Understanding the Assertion
The assertion states that an equilibrium is established between the generation and destruction of ozone, leading to a steady state concentration of the ozone layer in the stratosphere at an altitude of 20-30 km above sea level.

- **Explanation**: Ozone is formed in the stratosphere through the photodissociation of oxygen molecules by ultraviolet (UV) light, which then recombine to form ozone (O3). Simultaneously, ozone is destroyed by UV radiation as well. This balance between formation and destruction creates a steady concentration of ozone in the stratosphere.

### Step 2: Understanding the Reason
The reason states that the thickness of the ozone layer is generally larger above the equator and smaller above the poles.

- **Explanation**: The ozone layer is indeed thicker at the equator due to higher levels of UV radiation, which leads to more ozone formation. Conversely, the thickness is less at the poles because there is less UV radiation reaching those areas.

### Step 3: Evaluating the Relationship
Now we need to evaluate if the reason correctly explains the assertion.

- **Analysis**: While both the assertion and reason are true, the reason does not directly explain the assertion. The assertion discusses the equilibrium of ozone concentration, while the reason discusses the variation in thickness of the ozone layer based on latitude.

### Conclusion
- **Assertion**: True
- **Reason**: True
- **Explanation**: The reason does not adequately explain the assertion.

Thus, the correct answer is that both the assertion and reason are true, but the reason is not the correct explanation of the assertion.

### Final Answer
Both the assertion and reason are true, but the reason is not the correct explanation of the assertion.

---