Step-by-step explanation:
Sulphur dioxide is oxidised by the oxygen in the atmosphere to form sulphur trioxide, the major component in acid rain.
2SO2 + O2 - - > 2SO3
The subsequent Sulphur trioxide reacts with water in the rain/lake/river to form sulphuric acid.
SO3 + H20 - - > H2SO4
The sulphuric acid undergoes ionisation to form:
In major quantities ;
H2SO4 <----> H+ + HSO4-
And
In smaller quantities to form sulphate ion;
H2SO4 <---> 2H+ + SO4^-2