Distinguishing correct chemical definitions

Steps:

• Evaluate A: Empirical formula shows simplest atom ratio, not actual counts.
• Evaluate B: Molecular formula may match empirical if ratio is 1:1.
• Evaluate C: Concentration uses mol/dm³ for molarity but other units exist.
• Select D: Matches definition of relative atomic mass as average isotopic mass.

Why D is correct:

• Relative atomic mass is defined as the weighted average mass of an element's isotopes relative to 1/12 the mass of a carbon-12 atom.

Why the others are wrong:

• A: Empirical formula gives ratio, not actual atom numbers (e.g., glucose C₂H₄O₂ empirical, C₆H₁₂O₆ molecular).
• B: Molecular formula can equal empirical (e.g., water H₂O for both).
• C: Concentration can be expressed in g/dm³, %, or ppm, not only mol/dm³.

Final answer: D