Chemistry - Chemical Equilibrium Question with Solution | TestHub

Decomposition of${\mathrm{N}}_2{\mathrm{O}}_4\left(\mathrm{g}\right)$takes place as follows
${\mathrm{N}}_2{\mathrm{O}}_4\left(\mathrm{g}\right)\rightleftharpoons 2\mathrm{N}{\mathrm{O}}_2\left(\mathrm{g}\right)$
'D' is the vapour density at initial stage and 'd' is the vapour density at equilibrium. We get following graph when the degree of dissociation$\mathrm{\text{'}}\mathrm{\alpha }\mathrm{\text{'}}$is plotted against$\left(\frac{\mathrm{D}}{\mathrm{d}}\right)$

What is the value of$\frac{\mathrm{D}}{\mathrm{d}}$at A?