7.+Sources+hisham

http://www.chemicalelements.com/elements/o.html http://chemistry.about.com/od/elementfacts/a/oxygen.htm [|http://www.google.com/search?hl=en&q=oxygen+element&btnG=Google+Search\] http://www.noblemind.com/search.exe?keyword=Oxygen+Number+of+Protons&var=2