Answer:
A secondary pollutant
Explanation:
Pollutants can broadly be classified into two main categories based on their formation or synthesis. 1: Primary pollutants, 2: Secondary pollutants.
1: Primary pollutants
Primary pollutant can be considered as any environmental pollutant that is being directly emitted from a certain source like when we burn coal carbon di oxide is directly emitted into the atmosphere so CO2 is a primary pollutant.
Similarly sulfur di oxide or SO2 is also a primary pollutant that is emitted by the gas emissions of motor vehicles.
2: Secondary pollutants:
On the other hand, secondary pollutant is something that is not directly emitted on earth as an environmental pollutant but some how it is formed due to a reaction of primary pollutant.
Such as mentioned in the question that SO2 when oxidized in air in the presence of enzymes and water, it form H2SO4 or acid rain which directly falls on earth and incurs great amount of damage to not only living organisms but also non-living organisms such as marble buildings.
Therefore, acid rain is secondary pollutant. Please see picture for better understanding.
Hope it help!
