The compound that can undergo decomposition to produce magnesium oxide and water is magnesium hydroxide. The chemical formula for magnesium hydroxide is Mg(OH)2. When magnesium hydroxide is heated, it undergoes a decomposition reaction to form magnesium oxide (MgO) and water (H2O).

The chemical equation for the decomposition of magnesium hydroxide is:

Mg(OH)2(s) → MgO(s) + H2O(g)

In this reaction, magnesium hydroxide breaks down into magnesium oxide and water vapor. The magnesium oxide is a solid, while the water vapor is a gas.