RAS question
The chemical formula of ozone is:
Correct answer: (B) O3.
Ozone has the chemical formula O3 because each ozone molecule is made of three oxygen atoms.
Explanation
Ozone is not ordinary molecular oxygen; it is a triatomic form of oxygen, so its formula is O3. The EPA describes ozone as a highly reactive gas composed of three oxygen atoms and notes that it occurs in both the stratosphere and the troposphere. This explains the exam answer: the subscript 3 is essential because ozone contains three oxygen atoms in one molecule. In the stratosphere, ozone forms the ozone layer, which reduces harmful ultraviolet radiation reaching Earth. At ground level, the same gas is a pollutant, so the key is to identify the molecule first and then understand that its effect depends on where it is found in the atmosphere.
Why the other options are wrong
- (A) O2 is dioxygen, the ordinary molecular form of oxygen, while ozone has three oxygen atoms and is written as O3.
- (C) CO2 is carbon dioxide, a compound of carbon and oxygen, whereas ozone contains only oxygen atoms.
- (D) H2O2 is hydrogen peroxide, which contains hydrogen as well as oxygen, unlike ozone's three-oxygen-atom molecule.
Concept
This tests the basic Science and Technology concept of allotropes and atmospheric gases. It recurs in RAS because ozone links a simple chemical formula with environment topics such as the ozone layer, UV radiation and air pollution.