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Corrosion/tarnish of alloys: Brass gets discoloured in air due to the presence of which gas? Identify the gas that reacts with copper in brass to form a dark sulfide film. Choose the correct gas.

Difficulty: Easy

Hydrogen sulfide (H2S)
Oxygen (O2)
Carbon dioxide (CO2)
Nitrogen (N2)

Correct Answer: Hydrogen sulfide (H2S)

Explanation:

What is being asked?
The atmospheric gas responsible for the dark tarnish on brass.

Given data

Alloy: Brass (Cu + Zn)

Concept/Approach
H₂S in air reacts with copper to form copper sulfide films, causing discoloration; oxygen alone forms oxide patina more slowly, while CO₂ and N₂ are largely inert here.

Final Answer
Hydrogen sulfide (H₂S)

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