Magnesium reacting with steam. Water (H2O) soaked in mineral wool (far right) is being heated in the test tube. The magnesium (Mg) is reacting violently (black, centre right) with the steam. The reaction is giving off hydrogen gas (H2). The hydrogen gas flows out of the tube (far left), where it has been set alight. Magnesium belongs to group 2 of the periodic table and is a greyish- white, highly reactive metal. The equation for this reaction is: Mg + H2O ---> MgO + H2.