Which of the following describes atomic mass?

Rationale

Average mass of that element's isotopes.

Atomic mass is calculated as the weighted average of the masses of an element's naturally occurring isotopes, considering both their mass and relative abundance. This provides a more accurate representation of the mass of an atom as it appears in nature, rather than focusing on individual isotopes or particles.

A (Mass of protons and electrons) YOUR ANSWER

This choice inaccurately describes atomic mass. While protons contribute significantly to the mass of an atom, electrons have negligible mass in comparison. Furthermore, atomic mass does not solely depend on protons and electrons, as neutrons also play a crucial role in determining the total mass of an atom.

B (Mass of neutrons and electrons) YOUR ANSWER

This option is incorrect because it omits the mass of protons, which are essential components of an atom's nucleus and contribute significantly to its overall mass. Atomic mass is not defined solely by neutrons and electrons, as protons are equally important in establishing the mass of an atom.

C (Average mass of that element's isotopes) CORRECT

This is the correct answer because atomic mass specifically refers to the weighted average of the masses of all the isotopes of an element, taking into account their relative abundances. This definition encompasses the contributions of both protons and neutrons in the isotopes' nuclei, providing a comprehensive measure of atomic mass.

D (Number of moles in a solution) YOUR ANSWER

This choice is unrelated to atomic mass. The number of moles refers to the amount of substance in terms of quantity and is not a measure of mass. Atomic mass is concerned with the mass of individual atoms or isotopes rather than the concept of moles, which pertains to chemical quantities in reactions.

Conclusion

Atomic mass is defined as the average mass of an element's isotopes, calculated based on their relative abundances. This definition emphasizes the importance of both protons and neutrons in determining an atom's mass, while incorrect options either misrepresent the components contributing to atomic mass or stray into irrelevant concepts like moles. Understanding atomic mass is crucial for fields such as chemistry and physics, as it influences how elements interact and behave in various reactions.

Which of the following describes atomic mass?

Average mass of that element's isotopes.

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