Question

Find the average atomic mass of element X based on the isotope percentages:

80% of 64X
15% of 65X
5% of 66X

A) 64.5
B) 65.5
C) 66.5
D) 67.5

Answer 1

To calculate the average atomic mass of element X, the mass of each isotope is multiplied by its natural abundance and the results are added. The average atomic mass calculated is 64.25 amu, making answer A) 64.5 the closest choice.

Step-by-step explanation:

To find the average atomic mass of element X, you multiply the mass of each isotope by its natural abundance (expressed as a decimal), and then add these values together. In this case:

• (0.80 × 64 amu) = 51.2 amu
• (0.15 × 65 amu) = 9.75 amu
• (0.05 × 66 amu) = 3.3 amu

Adding these contributions gives us the average atomic mass of element X:

51.2 amu + 9.75 amu + 3.3 amu = 64.25 amu

Therefore, the closest answer to our calculated average atomic mass is A) 64.5.