Which of the following metals cannot replace hydrogen from water or steam?

Step 1: Analyze the question We need the metal that cannot displace hydrogen from water or steam. This is about the reactivity series.

Step 2: The concept A metal can replace hydrogen from water or steam only if it is above hydrogen in the reactivity series:

K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au

• Sodium reacts with cold water, vigorously: 2Na + 2H₂O → 2NaOH + H₂
• Magnesium reacts very slowly with cold water but burns in steam: Mg + H₂O(g) → MgO + H₂
• Iron reacts with steam when red-hot, and the reaction is reversible: 3Fe + 4H₂O(g) ⇌ Fe₃O₄ + 4H₂
• Copper is below hydrogen in the series, so it does not react with water or steam at all.

Step 3: Check each option

• A. Sodium: reacts with water, so it is not the answer.
• B. Magnesium: reacts with steam, so it is not the answer.
• C. Iron: reacts with steam, so it is not the answer.
• D. Copper: no reaction, so it is the answer.

Answer: D. Copper

Exam tip: Remember the series with the mnemonic "Please Stop Calling Me A Zebra, I Like Her Cute Smile Giraffe" (Potassium, Sodium, Calcium, Magnesium, Aluminium, Zinc, Iron, Lead, Hydrogen, Copper, Silver, Gold). Any metal after hydrogen, such as copper, silver or gold, will not liberate hydrogen from water, steam or dilute acids.