Answer: mass.
- A volume
- B mass
- C number of moles
- D density
Correct answer: B. mass
Explanation: Proust's law of definite (constant) proportions states that a pure compound always has the same elements combined in the same fixed ratio by mass.
Mass connects to moles via molar mass, and moles connect to particle count via Avogadro's number or to gas volume via the 22.4 L/mol rule at STP.
Concept context
The mole is chemistry's counting unit. Learn to relate mass, volume, and number of particles using Avogadro's number and molar mass, the foundation of all stoichiometry and reaction calculations.