$t=0 \quad 1 \quad 0 \quad 0$

$t_{e q} \quad  1-\alpha \quad x \alpha \quad y \alpha$

Total no. of moles $(i)=1-\alpha+x \alpha+y \alpha$

$i-1=x \alpha+y \alpha-\alpha$

$=\alpha(x+y-1)$

$\therefore \quad \alpha=\frac{i-1}{(x+y-1)}$