The degree of dissociation $(\alpha$) of a weak electrolyte $A_xB_y$ is related to vant Hoff factor (i) by the expression :

Question

( A ) $\alpha = \frac{i - 1}{(x+y+1)}$
( B ) $\alpha = \frac{(x+y-1)}{i - 1}$
( C ) $\alpha = \frac{i - 1}{(x+y-1)}$
( D ) $\alpha = \frac{(x+y+1)}{i - 1}$