Where
$w=0.85\,g$
$W=125\,g$
$\Delta {T_f}\, = \,0{\,^o}C\, - \,( - \,23{\,^o}C)\, = \,23{\,^o}C$
Now, $i\, = \,\frac{{{M_{normal}}}}{{{M_{observed}}}}\, = \,\frac{{136.3}}{{55}}\, = \,2.47$
$\mathop {ZnC{l_2}}\limits_{1 - \alpha } \, \rightleftharpoons \,\mathop {Z{n^{ + + }}}\limits_\alpha \, + \,\mathop {2C{l^ - }}\limits_{2\alpha } $
Van't Hoff factor $(i)$
$ = \,\frac{{1 - \alpha \, + \,\alpha \, + \,2\alpha }}{1}\, = \,2.47$
$\therefore \,\,\alpha \, = \,0.735\, = \,73.5\,\,\% \,$