Answer:
The natural abundance of Re-185 is 40% and of Re-187 is 60%
Explanation:
Relative atomic mass is defined as the sum of the mass of each isotope times its relative abundances.
Is Rhenium has only 2 isotopes and the abundances are X and Y we can write:
X + Y = 1 (1)
And:
185X + 187Y = 186.2 (2)
Where X is abundance of Re-185 and Y abundance of Re-187
Replacing (1) in (2):
185X + 187(1-X) = 186.2
185X + 187-187X = 186.2
-2X = -0.8
X = 0.4 = 40%
And Y = 100% - 40% = 60%
The natural abundance of Re-185 is 40% and of Re-187 is 60%
