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 :Let the PERCENTAGE of`""_(8)^(16)` X be x
Then the percentage of`""_(8)^(18)` X is (100-x )
`(16 xx (x)/(100)) + 18 xx ((100 - x)/(100)) = ` 16.2
`therefore (16x + 1800 - 18x )/(100) = 16.2`
`therefore - 2x + 1800 = 16.2 xx 100`
`therefore-2x + 1800 = 1620 `
`therefore - 2x = 1620 - 1800`
`therefore -2x =- 180`
`therefore x = 90`
The percentage of ISOTOP `" "_(8)^(16)` X is 90 and the of `""_(8)^(18)`X is 10.


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