The correct option is 1 and 3 only.
Explanation
Ozone ($O_3$) is a highly reactive gas composed of three oxygen atoms. It is found in two main layers of the atmosphere: the stratosphere (upper atmosphere) and the troposphere (ground level). Its impact on life and the environment depends entirely on its location.
Statement-wise Analysis:
- Statement 1 is Correct: Ozone is chemically formed by three atoms of oxygen. Its chemical formula is $O_3$. It is distinct from the diatomic oxygen ($O_2$) that humans breathe.
- Statement 2 is Incorrect: At ground level (the troposphere), ozone is not beneficial; it is a harmful air pollutant. It is formed by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. Ground-level ozone causes respiratory issues in humans and damages crops and vegetation.
- Statement 3 is Correct: In the upper atmosphere (the stratosphere), naturally occurring ozone creates a protective layer known as the "Ozone Layer." This layer absorbs and filters out the sun's harmful ultraviolet (UV) radiation, specifically UV-B and UV-C, protecting living organisms on Earth from radiation damage.
Key Takeaway:
There is a critical distinction between "Good Ozone" found in the stratosphere, which protects Earth from UV radiation, and "Bad Ozone" found in the troposphere, which is a toxic pollutant and a major component of photochemical smog.