**Avogadro’s Law offers Volume-Amount Relationship** of gases.

*Amadeo Avogadro* in 1811, put forward a relationship between volume of a gas to the number of molecules at constant temperature and pressure. This has now been accepted as a law and is known as **Avogadro law.**

** Avogadro’s law states that equal volumes of all gases under the same conditions of temperature and pressure contain equal number of molecules.** This means that as long as the temperature and pressure remain constant, the volume of the gas depends upon the number of molecules of the gas or amount of the gas.

*Mathematically, Avogadro’s law may be expressed as :*

V ∝ *n *( *p *and T constant)

or **V = k_{4} n **

where ‘

*n*’ is the amount of substance (number of moles).

*The number of molecules in one mole of a gas has been determined to be 6.022 × 10 ^{23} and is known as Avogadro constant.*

**This means that one mole of each gas at standard temperature and pressure will have the same volume. This is known as molar volume, Vm.**