(A) Sodium: Reacts violently with cold water, often catching fire or exploding as it produces hydrogen gas.(B) Calcium: Reacts vigorously with cold water, though less violently than sodium. The bubbles of hydrogen gas produced often cause the metal to float.(C) Iron: Is too unreactive to move the needle with liquid water (cold or hot). However, it will react when it comes into contact with steam (water vapor) at high temperatures.The reaction produces Iron (II, III) oxide and hydrogen gas:$3Fe(s) + 4H_2O(g) ⟶ Fe_3O_4(s) + 4H_2(g)$(D) Magnesium: Does not react with cold water, but it does react with hot water to form magnesium hydroxide and hydrogen.