# The atomic mass of element A is 63.6 atomic mass units. The only naturally occurring isotopes of element A are A-63 and A-65. What is the percent abundance in a naturally occurring sample of element A closest to?

The most abundant isotope is ""^63A.
The average isotopic mass is the weighted average of the mass of the individual isotopes. Because the quoted average, $63.6$ $\text{amu}$, is closer to ""^63A than ""^65A, the ""^63A isotope is the more abundant. Can you tell us which metal this element is?