K-40 is a natural radioactive isotope which c | vedclass

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(B) Mass of $K-40$ in $370 \ mg$ of $K = \frac{370 	imes 0.012}{100} \ mg = 0.0444 \ mg = 0.0444 	imes 10^{-3} \ g$. Number of moles of $K-40 = \fra

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$6.69 	imes 10^{17}$

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(B) Mass of $K-40$ in $370 \ mg$ of $K = \frac{370 	imes 0.012}{100} \ mg = 0.0444 \ mg = 0.0444 	imes 10^{-3} \ g$. Number of moles of $K-40 = \frac{	ext{mass}}{	ext{molar mass}} = \frac{0.0444 	imes 10^{-3} \ g}{40 \ g/mol} = 1.11 	imes 10^{-6} \ mol$. Number of atoms of $K-40 = 	ext{moles} 	imes N_A = 1.11 	imes 10^{-6} 	imes 6.022 	imes 10^{23} \approx 6.69 	imes 10^{17} \ 	ext{atoms}$.

$K-40$ is a natural radioactive isotope which constitutes $0.012\%$ of natural potassium. If a cup of milk contains $370 \ mg$ of $K$,how many atoms of $K-40$ are ingested?

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