Atomic mass — evaluate the definition “The atomic mass of an element is the number of times the atom of that element is heavier than the hydrogen atom.” Is this definition correct under the modern standard?

Introduction / Context:
Atomic and molecular masses are foundational for stoichiometry, gas laws, and thermodynamic property evaluation. Historically, hydrogen was used as a reference, but modern standards use the carbon-12 scale to avoid ambiguity from hydrogen isotopes and measurement issues.

Given Data / Assumptions:

• IUPAC standard defines the atomic mass unit (u) via carbon-12.
• Relative atomic mass (dimensionless) and molar mass (kg/mol) are related but distinct concepts.
• Isotopic composition influences standard atomic weights.

Concept / Approach:
The modern definition sets the mass of a carbon-12 atom to exactly 12 u. Relative atomic mass of an element is the weighted average of isotopic masses relative to 1/12 of carbon-12, not to hydrogen. Therefore, the statement tying atomic mass directly to a hydrogen atom is outdated and incorrect today.

Step-by-Step Solution:
Recognize the claim: comparison to hydrogen atom as reference.Recall the accepted standard: carbon-12 provides the reference for the atomic mass unit.Conclude the statement is false under the modern convention.

Verification / Alternative check:
Periodic tables list relative atomic masses on the carbon-12 scale (e.g., O ≈ 15.999, Fe ≈ 55.845) derived from isotopic distributions, confirming the standard.

Why Other Options Are Wrong:
Options C and D mischaracterize references; option E mixes a true factor (isotopes) with the wrong reference definition.

Common Pitfalls:
Confusing “atomic mass unit reference” with “arbitrary hydrogen reference”; mixing molar mass and relative atomic mass.

Final Answer:
False