Magnesium hydroxide (Mg(OH)₂) is classified as insoluble in water. Although it can dissolve to a small extent, the solubility is so low that it’s generally considered insoluble for practical purposes.
This low solubility is due to the strong ionic bonds between magnesium ions (Mg²⁺) and hydroxide ions (OH⁻), which require a significant amount of energy to break apart. When mixed with water, only a negligible amount of Mg(OH)₂ will dissociate into its ions, resulting in a very low concentration in solution.
In summary, while Mg(OH)₂ does have some degree of solubility, it is predominantly regarded as insoluble in water, which is why it is often utilized in various applications, such as an antacid, where its insolubility in digestive fluids is advantageous.