what is mean by the classification of the air.
what are the different types.and explain.

I’m assuming you are asking about clean room classifications.
They are in reference to the number and size of particles allowable in a given volume of air within a certain area classification. There are different classification systems by various bodies. Some of the main ones are disscussed and explained at the following web address (it’s a pdf page).

That page is from “The Scottish Society for Contamination control”. Thats just a result from a quick google search but it should at least give you a start to find out about each grade and system in more detail.