Explain: Avogadro's Law.

(N/A) In $1811$,Italian scientist Amedeo Avogadro combined the conclusions of Dalton's atomic theory and Gay-Lussac's law of combining volumes,which is now known as Avogadro's Law.
Avogadro's Law: It states that equal volumes of all gases under the same conditions of temperature and pressure contain an equal number of molecules.
Mathematical Formula: According to Avogadro's Law,as temperature and pressure remain constant,the volume depends upon the number of molecules of the gas,or in other words,the amount of the gas.
$V \propto n$ (constant $T$ and $p$) .....(Eq.-$i$)
where,$n =$ number of moles of the gas.
$V = k_4 n$ (Eq.-$ii$)
Molar volume at $STP = 22.7 \ L$.
Atoms in one mole $= 6.022 \times 10^{23}$.
The relation between volume and density of a gas can be obtained as $M = k_4 d$.
Calculation of moles of gas:
Gaseous mole $(n)$ $= \frac{\text{Weight of gas (} m \text{)}}{\text{Molecular mass of gas (} M \text{)}}$ ....(Eq.-$i$)
$\therefore n = \frac{m}{M}$
where,$m =$ weight of gas,$M =$ molecular mass of gas.
According to Avogadro's law formula:
$V = k_4 n$ ....(Eq.-$ii$)
$\therefore V = k_4 \frac{m}{M}$ .....(Eq.-$iii$)
Thus,$M = k_4 \left( \frac{m}{V} \right)$ .....(Eq.-$iv$)
Since,$\frac{m}{V} =$ density of gas $= d$
$\therefore M = k_4 d$ (Eq.-$v$)
Conclusion: The density of a gas is directly proportional to its molecular mass.