Answer:
The mass of the 185Re is 184.974 u
Explanation:
All elements in nature are present as mix several Isotopes. The Average Atomic mass is the weighted product of each Isotope times its specific atomic mass. Then, for the Rhenium:
[tex]62.20% * 186.956 u + (100% -62.20%) * 185ReAM = 186.207 u[/tex]
Where 185ReAM stands for the Atomic mass of the 185Re isotope. Then solving for this:
[tex]185ReAM=\frac{186.956 u-0.6220*186.956 u}{1-0.6220}=184.974 u[/tex]
Remember that 100%=1, 62.20%=0.6220