Question

an element has two naturally - occurring isotopes. isotope a has a mass of 63 amu with a percent abundance of 69.2%, and isotope b has a mass of 65 amu with a percent abundance of 30.8%. what is the average atomic mass of the element? 63.6 64.9 61.6 64.4

Explanation:

Step1: Convert percentages to decimals

$69.2\% = 0.692$, $30.8\%=0.308$

Step2: Calculate contribution of isotope A

$0.692\times63 = 43.596$

Step3: Calculate contribution of isotope B

$0.308\times65 = 20.02$

Step4: Find average atomic mass

$43.596 + 20.02=63.616\approx63.6$

Answer:

63.6