`Mg(OH)_(2)` is sparingly soluble in water but highly soluble in aqueous `NH_(4)Cl` solution-explain.

Explanation

`Mg(OH)_(2)` is a sparingly soluble ionic compound in aqueous solution, it exists in the following equilibrium:
`Mg(OH)_(2)(s)hArr Mg^(2+)(aq)+2OH^(-)(aq)`
Being a strong electrolyte, `NH_(4)Cl` dissociates almost completely in its aqueous solution to form `NH_(4)^(+) and Cl^(-)` ions `[NH_(4)Cl(aq)toNH_(4)^(+)(aq)+Cl^(-)(aq)]`. if `Mg(OH)_(2)` is added to `NH_(4)Cl` solution, then `NH_(4)^(+)` ions (produced from `NH_(4)Cl`) combine with `OH^(-)` ions [produced from `Mg(OH)_(2)`] to produce unionised weak base, `NH_(3)`. Consequently, the equilibrium involving dissociation of `Mg(OH)_(2)` shifts to the right and the solubility of `Mg(OH)_(2)` increases.
`Mg(OH)_(2)(aq)hArr Mg^(2+)(aq)+2OH^(-)(aq) overset(2NH_(4)^(+)(aq))hArr Mg^(2+)(aq)+2NH_(3)(aq)+2H_(2)O(l)`