PLEASE HELP How many moles of O2 are in the sample of 3.6 kilograms of air, if 21% of the air is oxygen O2 by mass?

Well to my expert knowledge and my exquisite calculations i think the the negative ion # 412 is the key to sucess

Ch4 and ph3 are both covalent since they are composed both of non-metals.    ch4 is non- polar because of  london forces and has a geometry of tetrahedral  ph3 , on the other hand, is umbrella shaped polar and has dipole-dipole intermolecular force (imf) . since ph3 is polar, it has a stronger imf   

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