SSC CGL 2024 Tier-I · 24 September 2024, Shift 2 · General Awareness · Question 10 of 100

Text as printed on a candidate's response sheet for this shift; answer per SSC's tentative key as marked on that sheet. Solution last reviewed 10 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. The questions and options here are reproduced as printed on a candidate's own response sheet for this shift — the Commission's text, unchanged. Each answer is SSC's tentative key as marked on that sheet; SSC allowed challenges to it and never publishes a final key. The solutions are written by UnlockIAS.

Which gas is evolved when iron and water react?

(a)Ammonia
(b)Oxygen
(c)Methane
(d)Hydrogen

Answer

Why

Correct — D. Iron sits above hydrogen in the reactivity series, so it displaces hydrogen from water. It does not react with cold or hot water, but it does react with steam:

3Fe + 4H₂O → Fe₃O₄ + 4H₂

The metal ends up as iron(II,III) oxide, Fe₃O₄, and the gas driven off is hydrogen, which is option (d).

Why the others are wrong

(a)
Ammonia — Ammonia needs a nitrogen source. Neither iron nor water supplies any nitrogen, so it cannot be a product here.
(b)
Oxygen — Oxygen is what the water gives up to the metal. It stays behind bound in Fe₃O₄ rather than coming off as a gas.
(c)
Methane — Methane needs carbon. No carbon enters this reaction, so no hydrocarbon can leave it.

Concept

How a metal treats water tracks its place in the reactivity series.

Sodium and potassium react violently with cold water.
Magnesium reacts with hot water.
Iron, aluminium and zinc react only with steam.
Copper, silver and gold do not react with water at all.

Wherever a reaction does happen the gas is hydrogen. What changes down the series is how hard you have to push to get it.

The stem says iron and water without naming steam. The reaction is real only with steam, so treat the condition as implied and answer on the product.

Key facts

Iron reacts with steam, not with cold or hot water, giving Fe₃O₄ and hydrogen.
3Fe + 4H₂O → Fe₃O₄ + 4H₂ is the standard equation for iron with steam.
A metal above hydrogen in the reactivity series displaces hydrogen from water or from an acid.
Sodium and potassium react with cold water, magnesium with hot water, iron and zinc only with steam.

Study next

The reactivity series and which metals react with cold water, hot water and steamMetal with dilute acid, and the burning-splint test for hydrogenIron oxides — Fe₃O₄ from steam against rust formed in moist air

Common traps

Answering oxygen because water contains it, when the oxygen is taken up by the metal.
Expecting iron to react with cold water and rejecting the reaction altogether.

The same displacement logic is set with a different reactant pair — zinc with sulphuric acid, again giving hydrogen, on 23 Sep 2024, 12:30, GA Q.9.

Related PYQs

No directly related past PYQ was found.