Which base is a metal hydroxide?

The correct answer is a metal hydroxide because it contains a metal (in this case, sodium) bonded to a hydroxide ion (OH⁻). Sodium hydroxide is classified specifically as a strong base and is often used in various applications, including cleaning agents and in the manufacturing of soaps.

Metal hydroxides generally consist of a metal cation combined with hydroxide anions, which contribute to their basic properties. In the case of sodium hydroxide, it readily dissociates in water to produce sodium ions and hydroxide ions, leading to increased pH and alkaline conditions.

In contrast, the other compounds listed do not fit the definition of a metal hydroxide. Sodium carbonate, magnesium sulfate, and calcium chloride are all salt compounds rather than bases. Sodium carbonate consists of sodium ions and carbonate ions, magnesium sulfate has magnesium ions and sulfate ions, and calcium chloride comprises calcium ions and chloride ions. None of these contain the hydroxide ion necessary to classify them as bases, particularly as metal hydroxides.