State and explain Dalton’s law of partial pressures.

“The total pressure exerted by a mixture of non reacting gases is equal to the sum of the partial pressures of individual gases”.
${\mathrm{P}}_{\left(\text{Total }\right)}={\mathrm{P}}_1+{\mathrm{P}}_2+{\mathrm{P}}_3+\dots \dots$
${\mathrm{P}}_1,{\mathrm{P}}_2,{\mathrm{P}}_3$ etc are partial pressures of gases.
Partial pressure in terms of mole fraction :
Suppose at the temperature T, three gases, enclosed in the volume V, exert partial pressure
P₁, P₂ and P₃ respectively.
${\mathrm{P}}_1=\frac{{\mathrm{n}}_1\mathrm{RT}}{\mathrm{V}}\Rightarrow {\mathrm{P}}_2=\frac{{\mathrm{n}}_2\mathrm{RT}}{\mathrm{V}};{\mathrm{P}}_3=\frac{{\mathrm{n}}_3\mathrm{RT}}{\mathrm{V}}$
According to Dalton’s law
$\begin{array}{l}\mathrm{P}={\mathrm{P}}_1+{\mathrm{P}}_2+{\mathrm{P}}_3=\frac{{\mathrm{n}}_1\mathrm{RT}}{\mathrm{V}}+\frac{{\mathrm{n}}_2\mathrm{RT}}{\mathrm{V}}+\frac{{\mathrm{n}}_3\mathrm{RT}}{\mathrm{V}}\\ =\left({\mathrm{n}}_1+{\mathrm{n}}_2+{\mathrm{n}}_3\right)\frac{\mathrm{RT}}{\mathrm{V}}\\ \mathrm{P}=\frac{\mathrm{nRT}}{\mathrm{V}}\left(\text{ Where }\mathrm{n}={\mathrm{n}}_1+{\mathrm{n}}_2+{\mathrm{n}}_3\right)\\ \frac{{\mathrm{P}}_1}{\mathrm{P}}=\frac{{\mathrm{n}}_1}{\mathrm{n}}={\mathrm{X}}_1\end{array}$
X₁ is called mole fraction of first gas.
$\mathrm{P}=\mathrm{X}\cdot {\mathrm{P}}_{\text{Total }}$