Derive the relation between the density of gases and their molecular mass using Avogadro's law.

(N/A) Calculation of moles of gas:
$n = \frac{m}{M}$....(Eq.-$i$)
where $m$ is the mass of the gas and $M$ is the molecular mass.
According to Avogadro's law,the volume $V$ is directly proportional to the number of moles $n$ at constant temperature and pressure:
$V = k n$....(Eq.-$ii$)
Substituting Eq.-$i$ into Eq.-$ii$:
$V = k \frac{m}{M}$....(Eq.-$iii$)
Rearranging for $M$:
$M = k \left( \frac{m}{V} \right)$....(Eq.-$iv$)
Since density $d = \frac{m}{V}$,we substitute this into Eq.-$iv$:
$M = k d$
Thus,the molecular mass of a gas is directly proportional to its density at constant temperature and pressure.