Good ozone is found in the

The correct option is stratosphere.

To understand why this is the correct answer, let us look at the structure of Earth's atmosphere and the role of ozone within it:

1. What is Ozone?
Ozone is a triatomic molecule consisting of three oxygen atoms ($O_3$). In the atmosphere, ozone can act as both a shield that protects life on Earth and as a pollutant, depending on where it is located.

2. "Good" Ozone vs. "Bad" Ozone
Atmospheric ozone is broadly divided into two categories based on its altitude:
• Stratospheric Ozone ("Good" Ozone): Roughly 90% of the Earth's ozone is found in the stratosphere, a layer of the atmosphere extending from about 10 to 50 kilometers (6 to 31 miles) above the Earth's surface. Here, it plays a vital role by absorbing the majority of the sun's harmful ultraviolet-B (UV-B) radiation. Without this protective shield, excessive UV radiation would reach Earth's surface, leading to increased rates of skin cancer, cataracts, and damage to terrestrial and aquatic ecosystems. Therefore, ozone in this region is considered "good."
• Tropospheric Ozone ("Bad" Ozone): The remaining 10% of atmospheric ozone is located in the troposphere, the lowest layer of the atmosphere (extending from the ground up to about 10 kilometers). Ground-level ozone is a key constituent of urban smog. It is a secondary pollutant formed when sunlight triggers chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs). It is toxic to humans, leading to respiratory illnesses, and harmful to vegetation. Therefore, ozone in this region is considered "bad."

3. Conclusion
Since "good" ozone refers to the protective ozone layer that filters harmful solar ultraviolet radiation, it is found in the stratosphere.