on the basis of Le chatelier's Principle explain why the addition of Solid NH4Cl to a saturated solution of Mg(OH)2 in water causes more of the Mg(OH)2 to dissolv

Explanation:

Le Chetelier's principle states that in an equilibrium system, if a constraint  (such as a change in pressure, temperature, or concentration of a reactant) is applied to the system, the equilibrium will shift so as to tend to annul the effect of the constraint. For the dissolution of Solid Magnesium oxide Mg(OH)2 in water, normally, only a small amount of the solid is dissolved to form magnesium ions Mg^2+ and hydroxide ions 2OH-. In a saturated solution of magnesium oxide in water, any action that removes the hydroxide ions formed will cause the reaction to shift to the product side on the right to favor the production of more hydroxide ion, which means more of the magnesium oxide will be dissolved.

Addition of Ammonium chloride NH4Cl neutralizes the hydroxide ions by acting as an acid, to form ammonia NH3 and water H20. This is because the Ammonium chloride dissolves to form ammonium NH4 and chlorine Cl^- ions in the solution, allowing the ammonium to react with the hydroxide ions. The reactions are shown below.

Mg(OH)2 ⇄ Mg^2+ 2OH^-     initial magnesium oxide dissolution

NH4Cl ⇒ NH4 + Cl     dissolution of ammonium chloride

NH4 + OH^- ⇒ NH3 + H2O   the consumption of the hydroxide ion by the ammonium to form ammonia and water, leading to more of the magnesium oxide dissolving to form more hydroxide ions.

since electrons are negative the answer is neagtaive