Question 34

Average mass of that element's isotopes

Atomic mass is defined as the average mass of an element's isotopes, taking into account the relative abundance of each isotope. This measurement reflects the weighted average of the different forms of an element that exist in nature.

A) Mass of protons and electrons

This option is incorrect as atomic mass specifically refers to the average mass of an element's isotopes, not just the mass of protons and electrons. While protons contribute significantly to atomic mass, electrons have negligible mass and do not define the atomic weight.

B) Mass of neutrons and electrons

This choice is also incorrect. Atomic mass does not solely account for neutrons and electrons. Similar to option A, neutrons contribute to the mass, but electrons have a minimal impact, and atomic mass is explicitly about the average of isotopes.

C) Average mass of that element's isotopes

This option is correct because atomic mass is indeed defined as the average mass of an element's isotopes, weighted by their natural abundance. This definition captures the essence of what atomic mass represents in the context of chemistry.

D) Number of moles in a solution

This option is incorrect as it refers to a completely different concept in chemistry. The number of moles in a solution pertains to the amount of substance present, rather than the average mass of isotopes that make up an element.

Conclusion

The correct answer, C, accurately describes atomic mass as the average mass of an element's isotopes, reflecting their natural occurrences. All other options fail to address the definition of atomic mass, either by misrepresenting the components involved or by referring to unrelated concepts in chemistry.