Relative atomic mass uses which standard for comparison?

Relative atomic mass uses which standard for comparison?

• A. 1/12th of the mass of a carbon-12 atom
• B. 1/12th of the mass of a carbon-14 atom
• C. The mass of a hydrogen atom
• D. The mass of an oxygen atom

Answer: (A)

Relative atomic mass is a way to compare how heavy an atom is using a single reference point. That reference point is set as 1/12 of the mass of a carbon-12 atom, so every element’s atomic mass is expressed as a ratio to that standard and has no fixed units. Carbon-12 is chosen because it’s a stable, well-defined isotope, which makes the standard reliable and consistent for all elements. The masses of elements are then treated as weighted averages of their isotopes, but still measured relative to that carbon-12 reference. Other options would shift the reference point to a different element or isotope, which would break this universally used scale, so they aren’t used as the standard.

Relative atomic mass is a way to compare how heavy an atom is using a single reference point. That reference point is set as 1/12 of the mass of a carbon-12 atom, so every element’s atomic mass is expressed as a ratio to that standard and has no fixed units. Carbon-12 is chosen because it’s a stable, well-defined isotope, which makes the standard reliable and consistent for all elements. The masses of elements are then treated as weighted averages of their isotopes, but still measured relative to that carbon-12 reference.

Other options would shift the reference point to a different element or isotope, which would break this universally used scale, so they aren’t used as the standard.