a
\((a)\) Van't Hoff factore \((i)\)

\(=\,\frac {No.\, of\, particles\, after \,association\, or \,dissociation}{No.\, of\, particles\, before\, association\, or \,dissociation}\)

For               \(M{X_2}\, \rightleftharpoons \,{M^{2 + }}\, + \,2{X^ - }\)

\(t\,=\,0\)             \(1\)              \(0\)              \(0\)

at.eq.                  \(1-\alpha \)       \(\alpha \)       \(2\alpha \)

Total no. of particles

\(=\,1\,-\,\alpha + \alpha +2\alpha \,=\,1+2\alpha \)

\(\therefore \) \(i\,=\,\frac {1+2\alpha }{1}\) \(=\,2\)

\(\therefore \alpha \,=\,0.50\) or \(50\%\)