For the dissociation of PCl5 s into PCI 3 and CI2 , in gaseous phase reaction, if d is the observed vapour density and D the theoretical vapour density with  α as degree of dissociation. Variation of D/d with 'αis given by which graph?

PCl5(g)⇌PCl3(g)+Cl2(g) t=0;      a            0           0 teq. ;     a-aα       aα         aα van't hoff factor, i=MTMo MT=iMo 2D=2id D=(aα+aα-aα+aa)d Dd=1+α α=Dd-1   If Dd⟶ at x-axis and (α)⟶ at y-axis  then it is a straight line positive slope and negative intercept.Where, MT=Theoretical Molar mass, Mo=Observed Molar mass.