MCQ Detailed View

The correct answer is Avogadro’s Law. This fundamental gas law explains that equal volumes of all gases, when measured at the same temperature and pressure, contain the same number of molecules. It does not matter what type of gas is being measured—oxygen, hydrogen, carbon dioxide, or nitrogen—the molecular count per unit volume remains equal under identical conditions.

Mathematically, Avogadro’s Law is expressed as:

V ∝ n (at constant T and P)

where V is the volume of the gas and n is the number of moles (or molecules). This means that if the number of molecules of a gas doubles, the volume will also double, provided that both temperature and pressure remain unchanged.

This principle forms the basis of the molar volume of a gas. At standard temperature and pressure (STP: 0 °C and 1 atm), one mole of any gas occupies 22.4 liters. This constant molar volume is widely used in chemical calculations, stoichiometry, and industrial applications.

Avogadro’s Law is also essential for deriving the Ideal Gas Equation (PV = nRT), which combines Boyle’s, Charles’ and Avogadro’s laws into one universal relation. It helps chemists and scientists in determining molecular masses, gas densities, and chemical reactions involving gases.

For example, in the reaction of hydrogen and oxygen to form water vapor, Avogadro’s Law helps balance the equation by comparing the reacting gas volumes. Similarly, it is applied in calculating the composition of mixtures and in analyzing gases in laboratories.

Thus, Avogadro’s Law provides a clear link between gas volume and the number of molecules, making it one of the most important laws in physical chemistry.