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Standard XII

Chemistry

Percentage Composition

Boron occurs ...

Question

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.

10, 90

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30, 70

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20, 80

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25, 75

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Solution

The correct option is C 20, 80
Let the percentage abundance of first isotope be $_{5}^{10} B = x$
Hence the percentage abundance of second isotope is $_{5}^{11} B = 100 - x .$

Avg atomic mass $=$ $\frac{x \times 10 + (100 - x) \times 11}{100}$
$1080 = 10 x + 1100 - 11 x$
or, $x = 20.$
Hence the %abundance of the two isotopes are 20 & 80 %.

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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.

The correct option is C 20, 80Let the percentage abundance of first isotope be 105B=xHence the percentage abundance of second isotope is 115B=100−x.Avg atomic mass = x×10+(100−x)×111001080=10x+1100−11xor, x=20.Hence the %abundance of the two isotopes are 20 & 80 %.