What are the uses of chemical fertilizers ?

Which of the following rotation of crops will reduce dependence on the use of chemical fertilizers?

A farmer is growing a crop regularly in his field. He uses chemical fertilizers, pesticides, organic manure as well as bio-fertilizers. Very close to his field is a factory which emits smoke as a by product. There is also a huge lake in the nearby area. An expert agriculturist suggests to the farmer to minimize the use of chemical fertilizers and instead use biofertilizers as they have many advantages over chemical fertilizers. Which of the following is NOT true for biofertilizers?

Nitrous oxide : I. occurs naturally in the environment II. is produced when fossil fuels are burnt III. quantity has increased due to the use of chemical fertilizers

How does chemical nature of the soil change due to continued use of chemical fertilizers ?

What are chemical fertilizers?

What are biofertilizers? In what sence are they better than chemical fertilizers?