${\mathrm{SO}}_3$ diffuses than ${\mathrm{SO}}_2$.

The van der Waal's equation of state for’n’ moles of real gases is $(\mathrm{P}+$$\mathrm{X}) \left(\mathrm{V}-\mathrm{nb}\right) =\mathrm{nRT}$. $\mathrm{X}$ can be_____.

$\mathrm{A}. \mathrm{X}=\frac{{\mathrm{n}}^2\mathrm{a}}{{\mathrm{v}}^2}, \mathrm{B}. \mathrm{X}=\frac{\mathrm{na}}{{\mathrm{v}}^2}, \mathrm{C}. \mathrm{X}=\frac{{\mathrm{n}}^2\mathrm{a}}{\mathrm{v}}$

"Enter the correct answer as $\mathrm{A}, \mathrm{B}$ or $\mathrm{C}.$"