What is the chemical formula for magnesium hydroxide?

The chemical formula for magnesium hydroxide is correctly represented as Mg(OH)₂. This formula indicates that each magnesium ion (Mg²⁺) pairs with two hydroxide ions (OH⁻) to form a neutral compound. The magnesium ion has a +2 charge, while each hydroxide ion has a -1 charge. Thus, to balance the overall charge, two hydroxide ions are needed for each magnesium ion, resulting in the formula Mg(OH)₂.

This understanding of the charges and the need for balance is crucial in determining the correct formula. The other options presented do not accurately reflect the composition of magnesium hydroxide. For instance, Mg(OH)₃ would imply an excess hydroxide ion for each magnesium, which does not occur in this hydroxide. Similarly, MgO represents magnesium oxide, which contains only magnesium and oxygen rather than hydroxide ions. Lastly, MgH₂O is not a valid chemical expression in this context, as it incorrectly suggests a relationship between magnesium and water without representing the correct hydroxide structure. Thus, the choice of Mg(OH)₂ is both chemically accurate and aligns with the ionic charges involved.