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NCERT Class XII Chapter
Nuclei
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Question : 2 of 31
Marks: +1, -0
The three stable isotopes of neon :
 1020Ne\,{}^{20}_{10}\mathrm{Ne} ,  1021Ne\,{}^{21}_{10}\mathrm{Ne} and  1022\,{}^{22}_{10} Ne have respective abundances of 90.51%, 0.27% and 9.22%. The atomic masses of the three isotopes are 19.99 u, 20.99 u and 21.99 u, respectively. Obtain the average atomic mass of neon.
Solution:  
Average atomic mass of neon with the given abundances,
A =
90.51(19.99 u)+0.27(20.99 u)+9.22(21.99 u)100\frac{90.51(19.99\,\mathrm{u})+0.27(20.99\,\mathrm{u})+9.22(21.99\,\mathrm{u})}{100} = 2017.7100\frac{2017.7}{100}
u = 20.18 u
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