Which of the following best describes the percent composition (mass percent) of a compound?

• A. The percentage by volume of each element in a compound relative to the total volume of the compound.
• B. The ratio of the molar mass of the compound to the molar mass of its elements.
• C. The percentage by mass of each element in a compound relative to the total mass of the compound.
• D. The ratio of the number of atoms of each element to the total number of atoms in the compound.

Answer: (C)

Verified step by step guidance

1. Understand that percent composition (mass percent) refers to how much each element contributes to the total mass of a compound, expressed as a percentage.
2. Recall the formula for percent composition by mass: \(\text{Percent composition of element} = \left( \frac{\text{mass of element in 1 mole of compound}}{\text{molar mass of compound}} \right) \times 100\%\).
3. Recognize that this concept focuses on mass, not volume or number of atoms, so options involving volume or atom count are incorrect.
4. Note that the ratio of molar masses or number of atoms does not directly give the percent composition by mass.
5. Conclude that the best description is the percentage by mass of each element relative to the total mass of the compound.