An undiscovered element has three naturally occurring isotopes of x-55, x-57, and x-58. isotope x-55 has an abundance of 27.80 % and isotope x-57 has an abundance of 44.39 %. what is the average mass of this element in amu?

The average atomic mass of this elements is 56.7221 amu.

Explanation: The average atomic mass is the sum of the masses of its isotopes each multiplied by their natural abundances.

           .....(1)

We are given 3 isotopes of an element.

For Isotope ,

Mass = 55 amu

Fractional abundance = 0.2780

For isotope ,

Mass = 57 amu

Fractional abundance = 0.4439

Total Fractional abundance = 1

For isotope ,

Mass = 58 amu

Fractional abundance = Total abundance - abundances of the other isotopes

Fractional abundance = 1 - 0.7219

                                     = 0.2781

Now, putting all the values in equation 1, we get

Average atomic mass = 56.7221 amu.