Q.Name the following.
The most abundant element in the universe.

Copper does not liberate H2 with dilute HCl (it is below H in the activity series).

A metal displaces hydrogen from a dilute acid only if it lies above hydrogen in the activity/electrochemical series. Zn, Na and Mg are all more reactive than hydrogen and liberate H2. Co …

Water gas is the industrial fuel mixture CO + H2, made by reacting steam with red-hot coke.

Water gas is prepared industrially by passing steam over red-hot coke (carbon) at about 1000 degrees C:

C(s) + H2O(g) --(~1000 degrees C)--> CO(g) + H2(g)

This reaction is endothermic, so the coke must periodically be reheated by blowing air through it (which regenerates the heat but also produces some "producer gas", a mixture of CO and N2, as a byproduct of that separate air-blast step). Water gas (CO + H2, roughly in 1:1 ratio) is itself an important industrial fuel and is also the key starting mixture ("synthesis gas") for manufacturing methanol and, via the water-gas shift reaction, additional hydrogen for ammonia synthesis.

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Zinc, being more reactive than hydrogen, displaces $H_2$ gas when it reacts with dilute sulphuric acid — the standard laboratory method for preparing hydrogen gas.

Step 1 — Recall the reaction:

$Zn(s) + dil.\ H_2SO_4(aq) \longrightarrow ZnSO_4(aq) + H_2(g)\uparrow$

This is a redox displacement reaction: Zn is oxidised ($Zn \to Zn^{2+} + 2e^-$) while $H^+$ ions are reduced ($2H^+ + 2e^- \to H_2$).

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Water gas is prepared by passing steam over red-hot coke; it is a mixture of carbon monoxide and hydrogen.

Water gas is manufactured industrially by passing steam over red-hot coke at about 1273 K:

C(s) + H2O(g) -> CO(g) + H2(g)

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Water gas is CO + H2, made industrially by passing steam over red-hot coke.

Note on syllabus scope: industrial preparation of hydrogen (including water gas) was taught under the Hydrogen chapter of the older NCERT syllabus, which has been dropped from the current rationalised CBSE Class 11 syllabus — flagged out-of-syllabus, answered honestly below.

Water gas is prepared industrially by passing steam over red-hot coke (carbon) at about 1273 K:

C(s) + H2O(g) → CO(g) + H2(g) (this is an endothermic, and also a redox, reaction: carbon is oxidised from 0 to +2, hydrogen is reduced from +1 to 0)

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