Which law, that was proposed in 1811, predicted that the same volume of gases at the same temperature and pressure would have the same number of molecules?

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This question was previously asked in

SSC CGL 2022 Tier-I Official Paper (Held On : 07 Dec 2022 Shift 1)

Answer 1

The correct answer is Avogadro’s law.

Key Points:

Avogadro proposed in 1811 that equal volumes of gases at the same temperature and pressure contain the same number of molecules.
According to this hypothesis, the relative molecular weights of any two gases are the same as the ratio of their densities under the same temperature and pressure conditions.
Avogadro also correctly deduced that simple gases were not made up of solitary atoms, but rather of compound molecules made up of two or more atoms.
(Avogadro did not use the term "atom"; at the time, the terms "atom" and "molecule" were almost interchangeable. He mentioned three types of "molecules," one of which was a "elementary molecule"—what we would call an atom.)
As a result, Avogadro was able to overcome the difficulty that Dalton and others had encountered when Gay-Lussac reported that the volume of water vapour above 100°C was twice the volume of oxygen used to form it.
According to Avogadro, the oxygen molecule split into two atoms during the formation of water vapour.

Additional Information:

Dalton’s law
- The overall pressure exerted in a mixture of non-reacting gases is equal to the sum of the partial pressures of the individual gases, according to Dalton's law, often known as Dalton's law of partial pressures. John Dalton discovered this empirical law in 1801 and made it public in 1802. The ideal gas laws are connected to Dalton's law.
Gay-Lussac’s law
- A gas law known as Gay-Lussac's law asserts that a gas's pressure (when kept at a constant volume and mass) varies directly with its absolute temperature. In other words, while the mass is fixed and the volume is constant, the pressure a gas exerts is proportional to the temperature of the gas.
Charles' law
- The experimental gas law known as Charles' law, commonly referred to as the law of volumes, illustrates how gases tend to expand when heated. Charles's law can now be stated as follows: When the pressure on a sample of a dry gas is held constant, the volume and Kelvin temperature will be in direct proportion.