Magnesium hydroxide (Mg(OH)₂) does dissolve in water to a very small extent, making it slightly soluble. It's considered practically insoluble for most practical purposes.

Here's why:

* Ionic compound: Mg(OH)₂ is an ionic compound, meaning it forms ions when dissolved in water.

* Low solubility: The solubility of Mg(OH)₂ is quite low. This means only a small amount of Mg(OH)₂ will dissociate into its ions (Mg²⁺ and OH⁻) when added to water.

* Equilibrium: The dissolution of Mg(OH)₂ is an equilibrium reaction. The process of dissolving and the process of the ions recombining back into solid Mg(OH)₂ happen simultaneously. The low solubility means the equilibrium lies heavily towards the solid Mg(OH)₂ side.

However, the solubility of Mg(OH)₂ can be increased by:

* Acids: Acids react with hydroxide ions (OH⁻) to form water, shifting the equilibrium towards further dissolution of Mg(OH)₂. This is why magnesium hydroxide is used as an antacid.

* Increased temperature: Solubility generally increases with temperature. While the effect is small for Mg(OH)₂, a slightly higher temperature will result in a slightly higher concentration of dissolved ions.

Overall: While Mg(OH)₂ does dissolve to some extent in water, it's considered practically insoluble. Its low solubility is due to the strong attraction between Mg²⁺ and OH⁻ ions, which keeps most of the compound in its solid form.