b
Mol.wt. \(\, = \,\frac{{{K_f}\, \times \,w\, \times \,1000}}{{\Delta {T_f}\, \times \,W}}\, = \,\) \(\frac{{1.86\, \times \,0.85\, \times 1000}}{{0.23\, \times 125}}\, \approx \,55\,gm\)

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 \((i)\)

\( = \,\frac{{1 - \alpha \, + \,\alpha \, + \,2\alpha }}{1}\, = \,2.47\)

\(\therefore \,\,\alpha \, = \,0.735\, = \,73.5\,\,\% \,\)