Calculate the average atomic mass for element X

39.02

Explanation:

From the question given above, the following data were obtained:

Isotope A:

Mass of A = 38

Abundance of A (A%) = 9.67%

Isotope B:

Mass of B = 39

Abundance of B (B%) = 78.68%

Isotope C:

Mass of C = 40

Abundance of C (C%) = 11.34%

Isotope D:

Mass of D = 41

Abundance of D (D%) = 0.31%

Average atomic mass of X =?

The average atomic mass of X can be obtained as follow:

Average = [(Mass of A × A%)/100] + [(Mass of B × B%)/100] + [(Mass of C × C%)/100] + [(Mass of D × D%)/100]

= [(38 × 9.67)/100] + [(39 × 78.68)/100] + [(40 × 11.34)/100] + [(41 × 0.31)/100]

= 3.6746 + 30.6852 + 4.536 + 0.1271

= 30.02

Thus, the average atomic mass of X is 39.02