Atomic Mass & Isotopic Abundance

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Problem

The element boron consists of two isotopes, ¹⁰₅B and ¹¹₅B. Their masses, based on the carbon scale, are 10.01 and 11.01, respectively. The abundance of ¹⁰₅B is 20.0%. What is the abundance of ¹¹₅B?

Solution

The sum of the abundances must equal 100%. Therefore:

abundance ¹¹₅B = 100.0 - 20.0 = 80.0%

Answer

80%

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