$$\begin{aligned} & \mathrm{MX}_2 \rightarrow \mathrm{M}^{+2}+2 \mathrm{X}^{-} \\ & \mathrm{i}=\frac{\text { normal molar mass }}{\text { observed molar mass }} \\ & \mathrm{i}=\frac{164}{65.6} \\ & 1+(3-1) \alpha=\frac{164}{65.6} \\ & 2 \alpha=\frac{98.4}{65.6} \\ & \alpha=0.75 \\ & \text { percent dissociation }=75 \% \\ & \text { Ans. } 75 \end{aligned}$$