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4. STRUCTURE OF THE ATOM
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If bromine atom is available in the form of, say, two isotopes $_{35}^{79}Br$ $(49.7 \%)$ and $_{35}^{81}Br$ $(50.3 \%),$ calculate the average atomic mass of bromine atom.
A
$0.80\,u $
B
$80.006\,u $
C
$89.006\,u $
D
$88.006\,u $
Solution
It is given that two isotopes of bromine are $_{35}^{79}Br$ $(49.7 \%)$ and $_{35}^{81}Br$ $ (50.3 \%) .$ Then, the average atomic mass of bromine atom is given by :
$79 \times \frac{49.7}{100}+81 \times \frac{50.3}{100}$
$=\frac{3926.3}{100}+\frac{4074.3}{100}$
$=\frac{8000.6}{100}$
$=80.006\,u $
Standard 9
Science
