Air contains 20% of O2 and 80 % N2 by moles find the average molecular mass weight and % by mass of oxygen and nitrogen.

Answer Key:  Mav = 23.8 amu ,  %  by mass of Oxygen =  22.3 %  and % by mass of Nitrogen is 77.7 % 

An element X have three isotopes X ^20 ,X ^21 and X ^22 . The percentage abundance of X^20 is 90% and the average atomic mass of element is 20.18. The percentage abundance of X ^21 should be

 Answer Key: 2%