Boron has two stable isotopes, 105B and 115B. Their respective masses are 10.01294 u and 11.00931 u, and the atomic mass of boron is 10.811 u. Find the abundances of 105B and 115B.

The atomic mass of the two isotopes of Boron (105B and 115B) are given as 10.01294 u and 11.00931 u


Let their abundances be respectively, x and (100-x) percent.


Hence from the formula discussed in previous question,


10.811 =


So, x = 19.89% and (100-x) = 80.11%


Hence the abundance of 10B5 is 19.89% and that of 11B5 is 80.11%


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