General Knowledge - General Science - Discussion

Why answer is B option?

The normal brown coloration on brass which slowly forms is primarily due to the oxidation of the copper (which makes up about 70% or more of the Brass alloy) to copper oxide. The greenish patina that forms on brass (especially in inclement environments) can be a complex of copper carbonates and acetates (acetates come from naturally or artificially occurring contaminants or droppings in the atmosphere depending on the presence of Industry).

Vinegar (acetic acid) is capable of producing an intense green corrosion on brass (copper acetate) and copper alloys generally. Regions near industry may be exposed to Sulfur compounds such as Sulfur Dioxide, or Hydrogen Sulfide. Both of these are potent copper oxidizers, hence the use of 'Liver of Sulfur' by artisans to oxidize copper, bronze, and brass castings.

Additionally Hydrogen Sulfide as well as liquid poly-sulfide concentrates are a potent oxidizer for Silver alloys as well. For this reason, do not keep your brass and silverware in a cabinet that also contains matches!

What is the disadvantage of nitrogen?

Why not carbon-dioxide is correct answer?

Should it be oxygen?

Hydrogen sulfide is a reducing agent and when brass comes in its contact reduction occurs and causes it discoloration being reactive and due to its acidic properties and oxygen and carbon dioxide can't do it. And it not present in dry air composition.

But you should not forget that some gases are present as pollutants and hydrogen sulphide is a primary pollutant and you cannot consider that the composition is always the same as it is described in books as pollutants are not considered while giving composition of dry air and more over moisture is there in air which helps in reduction of brass. As far as I understand and option B is the right option.

Why brass gets discolored when it reacts hydrogen sulphide?

Because when oxygen reacts with hydrogen chloride its get discolored.

But why can't it be nitrogen?

I can't understand, I think it's either A or B, I'm not sure about my answer.