Avogadro’s law (ideal gas mixtures and properties): Which statement correctly expresses Avogadro’s law?

Introduction / Context:
Gas laws summarize idealized relationships among pressure, volume, temperature, and amount. Avogadro’s law isolates the effect of the amount of substance by holding temperature and pressure constant and comparing volumes across different gases.

Given Data / Assumptions:

• Ideal gas behavior.
• Equal temperature and equal pressure conditions for comparisons.
• Use of amount in moles as the measure of quantity.

Concept / Approach:
Avogadro’s law states that equal volumes of different ideal gases at the same temperature and pressure contain the same number of molecules (moles). This leads directly to molar volume at standard conditions and underpins mixture relations like y_i = n_i/n_total. Dalton’s law (not Avogadro’s) treats additive partial pressures. The statement about gas constant and molecular mass relates to R_specific = R_universal / M, which, while true, is not Avogadro’s law.

Step-by-Step Solution:

Verification / Alternative check:
At STP, one mole occupies about 22.4 L (older) or 22.71 L (depending on convention), regardless of gas identity in the ideal limit.

Why Other Options Are Wrong:

• Option A: Property of specific gas constant, not Avogadro’s law.
• Option B: That is Dalton’s law of partial pressures.
• Option D: Includes incorrect or unrelated statements.

Common Pitfalls:
Confusing Avogadro’s and Dalton’s laws; mixing universal and specific gas constants.

Final Answer:
equal volumes of all gases, at the same temperature and pressure, contain equal number of molecules