Which of the following sets of elements are considered combustible metals?

• A. Magnesium, copper, and aluminum
• B. Magnesium, steel, and potassium
• C. Sodium, copper, and magnesium
• D. Sodium, potassium, and magnesium

Answer: (D)

Combustible metals are metals that can ignite and burn in air under certain conditions. Among common metals, sodium and potassium are highly reactive alkali metals that ignite in air when heated or finely divided, and they react violently with water. Magnesium also burns readily, producing a bright flame. Copper and steel do not burn in ordinary conditions, and aluminum resists burning due to its protective oxide layer. So the set that contains only metals known to burn is sodium, potassium, and magnesium.