There is a lot of stuff in that chap which I have never seen a question from. So please tell me the only topics which need to be studied from the chapter.
Very imp---Ppm concentration part ( safe level for drinking)
, BOD and stuff .
Well just read it once , anything can be asked from middle
And that smog and all that about the Taj Mahal becoming yellow
Those which are given.Like CFCs decomposition on light, those of ClO and No and radical and that ozone depletion things (polar stratospheric clouds) reactions. However what Pratyaksh said is more imp than reactions imo