Boron occurs in nature in the form of two isotopes having atomic mass 10 and 11. Calculate the percentage abundances of two isotopes respectively in a sample having atomic mass 10.80.
A
10, 90
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B
30, 70
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C
20, 80
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D
25, 75
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Solution
The correct option is C 20, 80 Let the percentage abundance of first isotope be 105B=x
Hence the percentage abundance of second isotope is 115B=100−x.
Avg atomic mass =x×10+(100−x)×11100 1080=10x+1100−11x
or, x=20.
Hence the %abundance of the two isotopes are 20 & 80 %.