What is acid rain? Discuss its harmful effects. 

Why does rain water normally have a pH of about 5.6? When does it become acid rain ?

What is the cause of acid rain? How is it harmful to the environment?

Statues and monuments in India are affected by acid rain. How?

Why is acid rain considered a threat to Taj Mahal?

What is green house effect and global warming?

What are the consequences of green house effect?
Or
What is the effect on the global warming due to the green house effect?

What is water pollution? What are the principal sources of water pollution?

What are the major causes of water pollution? Explain. 

What do you mean by BOD and COD? How are these determined?