1.

The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes ._(8)^(16)X and ._(8)^(18)X in the sample.

Answer»

Solution :It is given that the average atomic mas of the sample of element X is 16.2. LET the PERCENTAGE of isotope `._(8)^(18)X` be Y%. THUS the percentage of isotope `._(8)^(16)X` will be `(100-Y)%` therefore
`18xx(y)/(100)+16xx((100-y))/(100)=16.2`
`(18y)/(100)+(16(100-y))/(100)=16.2`
`(18y+1600-16y)/(100)=16.2`
`18Y+1600-16Y=1620`
`2Y+1600=1620`
`2Y=1620-1600`
`-Y=10`
Therefore the percentage of isotope of `._(8)^(18)X` is 10 %
And the percentage of isotope `._(8)^(16)X` is `(100-10)%=90%`.


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