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Physical Properties of Boron Family

Cu has only t...

Question

$C u$ has only two naturally occurring isotopes, $63_{C u}$ and $65_{C u}$ . If the atomic mass of $C u$ is $63.546$ , then the natural abundance of the $^{63} C u$ isotope will be approximately :

10 %

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30 %

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50 %

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70 %

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Solution

The correct option is D $70 %$
Let the natural abundance of $^{63} C u$ isotope be $x %$ .

The natural abundance of $^{65} C u$ isotope will be $100 - x$ .

The average atomic weight is $63.546$ g.
Hence, $100 \times 63.546 = 63 x + 65 (100 - x)$
$6354.6 = 63 x + 6500 - 65 x = 6500 - 2 x$
$2 x = 145.4$
$x = 72.7 ≃ 70$
Hence, the natural abundance of the $^{63} C u$ isotope must be approximately $70 %$ .

So, the correct option is $D .$

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Cu has only two naturally occurring isotopes, 63Cu and 65Cu. If the atomic mass of Cu is 63.546, then the natural abundance of the 63Cu isotope will be approximately :

$C u$ has only two naturally occurring isotopes, $63_{C u}$ and $65_{C u}$ . If the atomic mass of $C u$ is $63.546$ , then the natural abundance of the $^{63} C u$ isotope will be approximately :