Which one of the following metals burns if kept in air?

Sodium is an extremely reactive alkali metal that reacts vigorously with oxygen and moisture in the air, and can catch fire spontaneously. For this reason, sodium is stored under kerosene to prevent contact with air. Magnesium, zinc, and aluminium do not burn spontaneously when simply kept in air at room temperature — they require heating or ignition. Aluminium and zinc form protective oxide layers that prevent further reaction.