(a) Explain using an equation why rain falling in unpolluted air is acidic with a pH of about 5.7. 
Because it contains dissolved CO2
CO2 + H2O H2CO3 / CO2 + H2O H++ HCO3–
(b) “Acid rain” has a pH less than 5.6. Explain using an equation how the burning of coal can contribute to acid rain formation. 
Coal Contains Sulfur, burning it would give CO2
S + O2 SO2 / SO2 + H2O H2SO3
(c) “Acid rain” can affect plants and buildings.
(i) Outline how an acidic soil can damage the growth of trees. 
It leaches and removes nutrients (Ca2+, Mg2+, K+)
(ii) Give an equation for the reaction of acid rain on marble statues or limestone buildings. 
CaCO3 + 2H+ Ca2+ + CO2 + H2O
(d) Explain how the addition of calcium oxide to lakes could neutralize the effects of “acid rain”. 
CaO is a basic acid so it neutralize acid in lake
video link on acid desposition..
this video talks about the acid desposition in the air and atmosphere around us.