At `200^(@)C PCl_(5)` dissociates as follows :
`PCl_(5)(g0hArrPCl_(3)(g)+Cl_(2)(g)`
It was found that the equilibrium vapours are 62 times as heavy as hydreogen .The degree of dissociation of `PCl_(5)` at `200^(@)C` is nearly :
A. `10%`
B. `42%`
C. `50%`
D. `68%`