Answers

2014-05-13T15:28:43+05:30
1.51E24 atoms of oxygen are present in 2.50 moles and 3.01E24 atoms of 2.50 moles are present.
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2014-05-13T15:46:48+05:30
1 mole=6.023*10^23 atoms or molecules
2.5 moles=2.5*6.023*10^23 
                =15.0575*10^23 atoms or molecules
=>15.0575*10^23 atoms or molecules are present in 2.5 moles of O2.
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