Respuesta :


Let we have X of Tl-205 so the percent of Tl-203 will be 100-X

Average mass of  Thallium is 204.4

Mass of  Tl-205=[tex]\frac{X\times 205}{100}[/tex]  

Mass of  Tl-203=[tex]\frac{100-X\times 203}{100}[/tex]  

So,

[tex]\frac{100-X\times 203}{100}+\frac{X\times 205}{100}=204.4[/tex]  

205X +20300-203X=20440

X=70

So the percent or abundance of  Tl-205 is 70 while that of Tl-203 will be 30.