An element has three naturally occurring isotopes. the relative abundances of the isotopes are 0.27%, 9.25%, and 90.48%. the most abundant isotope has an atomic mass of 19.99 amu. the least abundant isotope has an atomic mass of 20.99 amu, and the remaining isotope has an atomic mass of 21.99 amu. based on these data, what is the average atomic mass of this element? (round your answer to the nearest hundredth and do not enter units in your answer.)

Answer

20.18

Explanation:

The atomic mass of X is the weighted average of the atomic masses of its isotopes.

We multiply the atomic mass of each isotope by a number representing its relative importance (i.e., its percent of the total).

Set up a table for easy calculation

0.9048 ×  19.99 u = 18.087   u

0.0027 × 20.99 u =  0.0567 u

0.0925 × 21.99  u =  2.0341  u

                TOTAL = 20.18      u

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