Accuracy of metal reactions with water and steam

Steps:

• Recall reactivity series: sodium > calcium > magnesium > iron.
• Note reactions with cold water: sodium and calcium react vigorously to hydroxides; magnesium and iron do not or very slowly.
• Note reactions with steam: magnesium and iron react when heated to oxides and hydrogen.
• Compare each option to standard chemical reactions.

Why B is correct:

• Iron reacts slowly with steam via 3Fe + 4H₂O → Fe₃O₄ + 4H₂, forming iron(II,III) oxide and hydrogen.

Why the others are wrong:

• A: Calcium reacts vigorously with cold water: Ca + 2H₂O → Ca(OH)₂ + H₂.
• C: Magnesium does not readily react with steam without ignition; it burns in air to form oxide, but steam reaction is not standard without heat.
• D: Sodium reacts with cold water to form sodium hydroxide, not oxide: 2Na + 2H₂O → 2NaOH + H₂.

Final answer: B