Question

Assume there only exist two stable isotopes of an element X. Element X-42 and X-44 exist in unknown abundances. Which of the following could possibly be the atomic weight of Element-X? Check all that apply.

A 41.52
B 42.84
C 43.13
D 43.82

Answer 1

Only options B (42.84) and C (43.13) could possibly be the atomic weights for Element X, as they lie between the weights of the two stable isotopes X-42 and X-44.

Step-by-step explanation:

The atomic weight of an element is the weighted average mass of all its naturally occurring isotopes. For an element with two stable isotopes, such as Element X consisting of isotopes X-42 and X-44, the atomic weight will be a weighted average based on the abundances of these two isotopes. The possible atomic weights must therefore be between the weights of the two stable isotopes. If we consider the four given atomic weights:

• A 41.52 (This is lower than the lightest isotope, so it cannot be correct.)
• B 42.84 (This is possible as it is between the weights of the two isotopes.)
• C 43.13 (This is also possible as it is between the weights of the two isotopes.)
• D 43.82 (This is higher than the weight of the heavier isotope, so it cannot be correct.)

Options B (42.84) and C (43.13) are the possible atomic weights for Element X. The other options are not possible as they fall outside the range of the isotope weights. This conclusion is similar to how the atomic mass of chlorine (Cl) is determined as a weighted average of its isotopes, like Cl-35 and Cl-37, which explain why chlorine's atomic mass is a non-whole number (35.45).