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The three stable isotopes of neon: `""_10^20"Ne"`, `""_10^21"Ne"` and `""_10^22"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.

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#### Solution

Atomic mass of `""_10^20"Ne"`, m_{1 }= 19.99 u

Abundance of `""_10^20"Ne"`, η_{1 }= 90.51%

Atomic mass of `""_10^21"Ne"`, m_{2 }= 20.99 u

Abundance of `""_10^21"Ne"`, η_{2 }= 0.27%

Atomic mass of `""_10^22"Ne"`, m_{3 }= 21.99 u

Abundance of `""_10^22"Ne"`, η_{3} = 9.22%

The average atomic mass of neon is given as:

`"m" = ("m"_1η_1 + "m"_2η_2 + "m"_3η_3)/(η_1 + η_2 + η_3)`

= `(19.99 xx 90.51 + 20.99 xx 0.27 + 21.99 xx 9.22)/(90.51 + 0.27 + 9.22)`

= 20.1771 u

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