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A piece of copper weighs $0.635g.$How many atoms of copper does it contain?

$\begin{array}{1 1} (A)\;6.02\times 10^{21} \\(B)\;7.03\times 10^{22} \\(C)\;2.03\times 10^{21} \\ (D)\;6.02\times 10^{17} \end{array}$

1 Answer

Gram-atomic mass of copper=$63.5g$
Number of moles in 0.635g of copper=$\large\frac{0.635}{63.5}$
$\Rightarrow 0.01$
Number of copper atoms in 0.01 moles =$0.01\times 6.02\times 10^{23}$
$\Rightarrow 6.02\times 10^{21}$
Hence (a) is the correct answer.
answered Oct 22, 2013 by sreemathi.v

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