Question

Consider an element Z that has two naturally occurring isotopes with the following percent abundances: The isotope with a mass number of 20 is 25% abundant. The isotope with a mass number of 22 is 75% abundant. What is the average atomic mass for element Z?

A. 2.0 amu
B. 20.5 amu
C. 21.0 amu
D. 21.5 amu

Answer 1

The average atomic mass of element Z is 21.5 amu.

Step-by-step explanation:

The average atomic mass for an element can be calculated by multiplying the mass of each isotope by its percent abundance and then adding all the values together. In this case, the element Z has two isotopes: one with a mass number of 20 and 25% abundance, and another with a mass number of 22 and 75% abundance. To calculate the average atomic mass, we can use the following equation:

Average atomic mass = (mass of isotope 1 x abundance of isotope 1) + (mass of isotope 2 x abundance of isotope 2)

Plugging in the values:

Average atomic mass = (20 x 0.25) + (22 x 0.75) = 5 + 16.5 = 21.5 amu

Therefore, the average atomic mass for element Z is 21.5 amu. So, the correct answer would be D. 21.5 amu.