Correct Option
The correct option is (c) 1 and 3 only.
Explanation
Ozone ($O_3$) is a triatomic molecule consisting of three oxygen atoms. It is an unstable gas with strong oxidizing properties, making it highly effective in water treatment processes for purification and disinfection.
Statement-wise Analysis
- Statement 1 is Correct: Ozone is widely used in water treatment as a potent disinfectant. Due to its high oxidation potential, it effectively kills bacteria, viruses, and protozoa by rupturing their cell walls. It is often preferred over chlorine because it does not leave harmful chlorinated by-products.
- Statement 2 is Incorrect: Aquatic animals require Dissolved Oxygen ($O_2$) for respiration, not Ozone ($O_3$). Ozone is chemically distinct from the diatomic oxygen used for breathing. In fact, high concentrations of residual ozone in water can be toxic to aquatic life, damaging fish gills and other tissues.
- Statement 3 is Correct: Ozone is an allotrope of oxygen. While stable oxygen exists as diatomic molecules ($O_2$), ozone exists as triatomic molecules ($O_3$). One of its fundamental physical properties is the ability to absorb ultraviolet (UV) radiation, which is the primary function of the stratospheric ozone layer.
Key Takeaway: Ozone is a powerful oxidizing agent and disinfectant used to purify water, but it is distinct from Dissolved Oxygen ($O_2$) and cannot support the respiration of aquatic organisms.