The unit of Van Der Waals gas equation parameter 'a' in $\begin{array}{l}\left(\mathrm{P}+\frac{{\mathrm{an}}^2}{{\mathrm{v}}^2}\right)(\mathrm{V}-\mathrm{nb})=\mathrm{nRT}\end{array}$

$\begin{array}{l}\left(\mathrm{P}+\frac{{\mathrm{a}}^2}{{\mathrm{v}}^2}\right)(\mathrm{v}-\mathrm{nb})=\mathrm{nRT}\end{array}$

Pressure correction value is equals 

$\frac{{\mathrm{an}}^2}{{\mathrm{v}}^2}$

$\mathrm{a}=\mathrm{atm}\times \frac{{\mathrm{lit}}^2}{{\mathrm{mol}}^2}$

$1\mathrm{lit}=1{\mathrm{dm}}^3$

$\mathrm{a}=\mathrm{atm}\times \frac{{\mathrm{dm}}^6}{{\mathrm{mol}}^2}$

Hence the required answer is D