`PCl_5` decomposes as `PCl_5(g) hArr PCl_3(g)+Cl_2(g)`.If at equilibrium , total pressure is P and density of gaseous mixture is d at temperature T then degree of dissociation `(alpha)` is :
(Molecular wt. of `PCl_5=M`)
A. `alpha=1-(PM)/(dRT)`
B. `alpha=1-(dRT)/(PM)`
C. `alpha=(PM)/(dRT)-1`
D. `alpha=(dRT)/(PM)-1`
