General Knowledge - General Science - Discussion

1. 

Brass gets discoloured in air because of the presence of which of the following gases in air?

[A]. Oxygen
[B]. Hydrogen sulphide
[C]. Carbon dioxide
[D]. Nitrogen

Answer: Option B

Explanation:

No answer description available for this question.

Umesh said: (Oct 4, 2010)  
Why we choose hydrogen sulphide?

Paras said: (Nov 8, 2010)  
Because it performs bleaching action probably.I'm not sure however!!

Yashwanth said: (Nov 16, 2010)  
Why cant other can perform it?

Dhanpal Singh said: (Nov 16, 2010)  
Because of chemical reaction.

Ramya said: (Dec 6, 2010)  
I think right ans is option A.

$Shivansh.Rathod$ said: (Dec 13, 2010)  
It is because the presence of mixture of hydrogen and sulphide and brass is a type of thing which has a color very light and mixture is non temperature (hot and cold type of temperature) so it gets discolored.

Nithesh said: (Jan 13, 2011)  
I think it is nature of atmosphere.

Ramyaramaraj said: (Jan 25, 2011)  
It is react with the atomsphere air,then it become colourless due to the effect of sulphide.

Bikash Panigrahi said: (Feb 8, 2011)  
It's due to the sulphide action.

Rajendra said: (Feb 14, 2011)  
It is one of the nature.

Md.Imran said: (Apr 3, 2011)  
It is because the presence of mixture of hydrogen and sulphide and brass is a type of thing which has a color very light and mixture is non temperature (hot and cold type of temperature) so it gets discolored.this is better answer.etc

Pravesh Sharma said: (Apr 5, 2011)  
I think that option a is correct because O2 can react with brass and can discolored it

Ankush Thakur said: (Apr 7, 2011)  
Presence of air and water in atmosphere.

Ruhi Khan said: (Apr 14, 2011)  
Actually transition elements are colored elements. Here Zn & Cu are the transition elements ,these composition is the brass. But it gets discolored in air because of presence of Hydrogen sulphide in the air.It discolored the color of the brass. So it appears as discolored.

Hina said: (Apr 23, 2011)  
Option b is correct.

Shivani said: (Apr 29, 2011)  
Becuse it is a chemical reaction so it discolored the color of the brass.

Srinivas Jntv said: (May 4, 2011)  
Transition elements are coloured. The brass is combination of zn and cu. But it is discoloured due to hydrogen sulphide in air.

Tsering said: (May 14, 2011)  
As we know that zinc and copper is substituent of the brass so they get reacted with hydrogen sulphide. Also compare to other hydrogen sulphide is more electronegative.

Balwinder said: (May 14, 2011)  
Any metal gets discolor due to its oxidation. Brass gets discolored in air due to the presence of Oxygen.

Pawani Kumari said: (May 21, 2011)  
Brass constitute zinc and copper and these two elements are transition elements. Among the given options hydrogen sulphide is more electronegative. So when it react with brass, brass get discolored.

Yashasvi said: (May 30, 2011)  
Hydro sulphide is a colourless gas and if mixed with others, will get colourless.

Anand Sharma said: (Jun 3, 2011)  
Actually brass constitutes of Cu+Zn, as it comes in contact of Hydrogen Sulphide, it transform into copper sluphate of blue color & zinc hydooxide of faint red color. Hence, it changes color.

Dev said: (Jun 19, 2011)  
The Cu present in brass reacts with the sulphide ion of H2S forming CuS (cupric sulphide) which is black colored. Thus when brass is exposed to air it gets discolored.

Sushma said: (Jun 25, 2011)  
I think B is the correct option Since the brass is an alloy of transition elements Zn and Cu,it reacts with hydrogen sulphide to get discolored

Paritosh said: (Jul 21, 2011)  
What is hydrogen sulphide? why should we choose it ?

Hardik said: (Aug 14, 2011)  
This process due to oxydation.

That's why I think answer is oxigen and oxigen must be present in process.

Jeeva said: (Aug 22, 2011)  
The Cu present in brass reacts with the sulphide ion of H2S forming CuS (cupric sulphide) which is black colored. Thus when brass is exposed to air it gets discolored.

Rajdeep said: (Oct 30, 2011)  
Give chemical reaction.

Bharat said: (Oct 31, 2011)  
Brass constitute zinc and copper and these two elements are transition elements. Among the given options hydrogen sulphide is more electronegative. So when it react with brass, brass get discolored.

Sahil Khare said: (Nov 14, 2011)  
Hydrogen gas gives a smell of rotten eggs and turns lead acetate paper silvery back.

Anushadevi said: (Dec 3, 2011)  
Because of the presence of hydrogen sulphide in Brass,it combines with oxygen in air and form water,evaporates.So remained sulphide is colourless in air .So Brass gets discoloured in the air.

Dinesh said: (Dec 7, 2011)  
Hydrogen sulphide can corrode metals such as iron, copper, brass. That discolour copper & brass utensils.

Sanjay said: (Jan 18, 2012)  
I think answer is "a' because it will form oxides with metals.

Karthik said: (Jan 31, 2012)  
Hydrogen sulphide-Hs+br->hbr+s.

So it become discolour.

Sahana said: (Feb 29, 2012)  
How its possible air doesn't have hydrogen sulphide?

Manuangel said: (Mar 2, 2012)  
Why we choose hydrogen sulphide. You mean hydrogen can do any material to decolourize?

Abcdef said: (Apr 5, 2012)  
How we can learn to balace reactions for class 8th?

Rani said: (Apr 13, 2012)  
Brass is a alloy so it can decolourise easily with hydrogen sulphide.

Prani said: (May 28, 2012)  
Brass is an alloy of Cu and Zn, when it comes in contact with H2S it forms zns and Cu2s which are black in colour hence brass gets discolured.

Ankit said: (Jun 4, 2012)  
Brass is a alloy of Cu and Zn so it can decolourise easily with hydrogen sulphide.

Renuka said: (Jun 11, 2012)  
Brass is a alloy so it can decolourise easily with hydrogen sulphide. .

Renuka said: (Jun 12, 2012)  
Cu present in brass reacts with h2s & undergo corrosion i.e. Its get oxidised hence ultimately get discolourised.

Apoorva said: (Jun 16, 2012)  
I think as brass has got zinc in it and it rapidly reacts with zinc and gets discolored.

Venkat said: (Jun 30, 2012)  
In air mixing the salt. In nature of salt properties.

Ramesh Naik Dhanavath said: (Jul 2, 2012)  
Primary ingredients of of brass are Copper&zinc. When brass exposed to air the hydrogen sulphide in the atmosphere is react with copper&zinc.

Copper reacts with sulphide ion and forms cupric sulphide which is black in color where as zinc reacts with hydrogen and forms zinc hydroxide which is faint red in color. Hence brass gets discolored when it exposed to air.

Antriksh said: (Aug 18, 2012)  
I think brass is the combination of copper also and it is reacts sulphor fast other than all these also zinc present in brass reacts with hydrogen but no any mixer reacts directly with the air whenever moisture is not present.

Raju Mandal said: (Sep 6, 2012)  
Brass is alloy of Cu and Zn. When it reacts with hydrogen sulfide(H2S).
It forms Cu2S(which is black in color) and ZnH2(which turns greyish on exposure to air at room temp). Hence answer is hydrogen sulfide

G Urudatt said: (Sep 11, 2012)  
Bars is made of cu and zn. Brass is a elements of transitee.

Rahulramesh said: (Sep 21, 2012)  
Any metal is discoloured in the process of oxidisation.

Aoke Soe Paing said: (Oct 3, 2012)  
The question is "which of the following gases". So the answer may be two or more gases. I think that as both of oxygen and H2S are in the air.

Yochana said: (Oct 8, 2012)  
How can you say that H2S is present in the atmosphere?

Jyothi said: (Oct 11, 2012)  
Becuase of oxidation any metal is discoloured in the process of oxidation.

Nepal Ranjan said: (Oct 22, 2012)  
Primary ingredients of brass are cu& zn. When brass exposed in the air then H2S reacts. Cu reacts with Sulphide forms cu2s which is colored black and zn reacts with hydrogen forms zinc hydroxide which color is faint red. That's why it gets discolored exposed in air.

Gauri said: (Dec 6, 2012)  
As brass is an alloy of copper and zinc, the copper when kept free to air reacts with hydrogen sulphide and so the alloy is discoloured.

Shashikant said: (Jan 10, 2013)  
As brass is metal made up from copper and zink it gets rusted from h2s present in air.

Swayamprava Dikshit said: (Jan 17, 2013)  
brass is an alloy of zn & cu. in present of atmosprere it reacts as
zn+cu+h2s=cu2s+znh.
cu2s coloured the alloy black & znh brings colours of faint red.

Purvi said: (Jan 23, 2013)  
Its a hydrogen sulphide which discolours the brass which is a composition of cu and zn.

Ashish Mishra M.Pharm said: (Apr 11, 2013)  
Because in the present of hydrogen sulphite in air cause oxidation reaction hence colour is change.

Shrinu said: (Apr 18, 2013)  
It is B presence of hydrogen sulphide in air and reacts oxidation then colour changes.

Dipali Dhakoliya said: (Apr 23, 2013)  
In brass the aluminium is present which is less reactive then hydrogen sulfide and it lose the colour.

Ananya Thakur said: (May 27, 2013)  
I am very intrested in science but I don't understand anything but I think option B is correct.

Stylish said: (Jun 20, 2013)  
Zinc and copper (mostly copper) oxidizes in air to form white zinc oxide and red copper oxide.

Supreem said: (Jun 25, 2013)  
Why brass discolored in the presence of hydrogen sulphide?

Please describe this?

Chandan Kumar said: (Jun 29, 2013)  
It gets discolored in air because of presence of Hydrogen sulphide in the air Brass constitute zinc and copper and these two elements are Hydro sulphide is a colourless gas and if mixed with others, will get colourless.

Poonam said: (Aug 1, 2013)  
Because brass is metal it get react with sulphide.

Karamvir said: (Aug 13, 2013)  
Brass react with hydrogen sulphide results hot and cold condition so it becomes colourless.

Nidhi said: (Aug 27, 2013)  
I think because other options are less reactive than H2s, and it reacts to give that colour.

Sra1 said: (Sep 6, 2013)  
Oxygen is correct because it easily reacts with corban compounds due to that it changes its colour.

Nag3 said: (Sep 14, 2013)  
It is H2 sulfide because brass contain them since it is an alloy made of it and tin.

Abhigna said: (Nov 13, 2013)  
I think it will not discolour. It may become black in colour, because of the presence of CU and Zn. If it react with H2S it forms CuS AND ZnS.

Akhildixit said: (Dec 8, 2013)  
When copper are colour less they are oxidize.

Beatrice said: (Jan 3, 2014)  
First we have to remember what are the components of brass?

Jyoti Prakash Panda said: (Jan 14, 2014)  
Safe corrosion will look reddish, black to brown or green to blue. Safe corrosion will occur if the brass has been kept clean and dry. If it is brownish or black this will be due to oxidization of the copper which occurs when exposed to air; this a natural phenomenon and is non-destructive. This is usually called "tarnish" and can be removed by careful cleaning and polishing. If the corrosion is green, continuous and non-flaky this again is safe corrosion.

Shailendra said: (Jan 24, 2014)  
Hydrogen sulphide is answer it reacts with metal.

Pranab Nath said: (Mar 24, 2014)  
Hydrogen sulphate is correct answer.

Sravya said: (Apr 10, 2014)  
I think the acidity of Hydrogen Sulphide is more than the oxygen. Because of that Brass can be easily discolored.

Dnyanesh Unawane said: (Apr 21, 2014)  
Hydrogen sulphide is having better bleaching ability.

Archita said: (Apr 21, 2014)  
Is the Hydrogen Sulphide more corrosive in nature?

Lingaswamy said: (May 4, 2014)  
According to my knowledge when sulphuric reacts with brass that surface will eats away with that when light falls on that light oriented in different direction so that we can't get any color appear there thats we may get black color.

My think so.

Sawmiya said: (May 13, 2014)  
Answer B is correct because brass is a material (Cu+Zn=brass) H2SO4 is acid so the brass is discoloured.

Meena said: (May 18, 2014)  
I think it must be a certain new type of reaction.

Paras said: (May 22, 2014)  
Ya option B is correct due to brass chemical compound and physical behaviour.

Raja Rupendra said: (Jun 11, 2014)  
Because it is better rathering with hydrogen sulphide.

Mita Sen said: (Jun 29, 2014)  
H2S is present in atmosphere?

Sandeep Singh said: (Jul 1, 2014)  
Hydrogen sulphide is (sulphur and oh-) so it is base and there is ph value is more than 7 so it is react with brass presence of air and discoloured the brass so hydrogen sulphide is right answer.

Anu said: (Jul 12, 2014)  
Yes it is as hydrogen sulphide clears the chlorophyll from the sensitive plants and plants which are found in hilly regions.

Upender said: (Sep 3, 2014)  
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.

Mitu Moharana said: (Oct 24, 2014)  
Its due to sulphide only.

Satyendra Pal said: (Oct 29, 2014)  
Option is A because oxygen gas is present in air.

Nirmaljeet Kaur said: (Nov 7, 2014)  
It is due to oxygen so the answer is A.

Priya said: (Dec 9, 2014)  
Option b is the answer because it removes the chlorophyll from plants.

Physic said: (Dec 28, 2014)  
When object is place between focus and optical center.

Scholar said: (Dec 30, 2014)  
In most of the answers it is said that sulphur reacts with brass but it cannot be ignored that hydrogen sulphide is a compound sulphur not only can react with brass.

Science Genius said: (Jan 9, 2015)  
Oxygen makes metal corrode, so I think A might be a right answer too.

Manik Sambyal said: (Jan 30, 2015)  
Hydrogen sulfide:

Chemical Compound:
Hydrogen sulfide is a chemical compound with the formula H 2S. It is a colorless gas with the characteristic foul odor of rotten eggs; it is heavier than air, very poisonous, corrosive, flammable, and explosive.

Formula: H2S.
Molar mass: 34.0809 g/mol.
Density: 1.36 kg/m^3.
Boiling point: -60 °C.
Melting point: -82 deg;C.
Soluble in: Water.
Classification: Sulfide, Sulfur compounds.

Sakshi Kawale said: (Mar 6, 2015)  
It is due to sulphide only.

Ciel Phantomhive said: (Mar 22, 2015)  
Hydrogen sulfide is a chemical compound with the formula H2S. It is a colorless gas with the characteristic foul odor of rotten eggs; it is heavier than air, very poisonous, corrosive, flammable, and explosive.

Hydrogen sulfide often results from the bacterial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers; this process is commonly known as anaerobic digestion H.

2S also occurs in volcanic gases, natural gas, and in some sources of well water. It is also present in natural halite type rock salts, most notably in Himalayan Black Salt, which is mostly harvested from the mineral-rich "Salt Range" mountains of Pakistan.

The human body produces small amounts of H2S and uses it as a signaling molecule.

Chelesa said: (Apr 30, 2015)  
I choose B because sulphide is a chemical which is very hot, so it heat things.

Nomit said: (May 9, 2015)  
I think B is the correct answer because H2S affect both silver and brass due to chemical reaction.

Ashutosh Mohapatra said: (May 13, 2015)  
I think the correct answer is option A. Because oxygen is a carrots.

Subroto Deb said: (May 16, 2015)  
Could any one reason for this answer?

Sonali said: (May 26, 2015)  
I think that answer B is correct because brass is equal to Zn and Cu which is transition element. We know that such types of elements are color elements. But when brass reacts with hydrogen sulphide it becomes discolored due to the presence of air.

Tejashwini said: (May 26, 2015)  
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 polysulfide 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!

Shashwat Rawat said: (May 26, 2015)  
Zinc which is present in brass reacts with hydrogen sulphide to form zinc sulphide which is black in colour.

Chidi said: (Jun 6, 2015)  
I never believed it was hydrogen sulphide.

K. Poorna Chandra Rao said: (Jun 15, 2015)  
Composition of Dry Air.

Substance % by volume.

Nitrogen, N2 78.08.
Oxygen, O2 20.95.
Argon, Ar 0.93.
Carbon dioxide, CO2 0.033.
Neon, Ne 0.0018.
Helium, He 0.00052.
Methane, CH4 0.0002.
Krypton, Kr 0.00011.
Nitrogen (I) oxide, N2O 0.00005.
Hydrogen, H2 0.00005.
Xenon, Xe 0.0000087.
Ozone, O3 0.000001.

In air H2S won't exists directly in air. Then how it will react?

K. Poorna Chandra Rao said: (Jun 15, 2015)  
Composition of Dry Air.

Substance % by volume.

Nitrogen, N2 78.08.
Oxygen, O2 20.95.
Argon, Ar 0.93.
Carbon dioxide, CO2 0.033.
Neon, Ne 0.0018.
Helium, He 0.00052.
Methane, CH4 0.0002.
Krypton, Kr 0.00011.
Nitrogen (I) oxide, N2O 0.00005.
Hydrogen, H2 0.00005.
Xenon, Xe 0.0000087.
Ozone, O3 0.000001.

In air H2S won't exists directly in air. Then how it will react?

Xyz said: (Jun 24, 2015)  
I think it should have been oxygen. But @Poorna Chandra is right, how will it react ?

Pathar Jignesh said: (Jun 29, 2015)  
I can't understand.

Ranasumit5786@Gmail.Com said: (Jul 12, 2015)  
Due to atmospheric pressure.

Tashad said: (Aug 21, 2015)  
Because it is homogeneous.

Pavan said: (Aug 21, 2015)  
H2s is superconductor also.

Sai Mahesh said: (Sep 13, 2015)  
Actually hydrogen sulfide is a oxidizing agent so when the bras is oxidize with hydrogen sulfide its convert to brass oxide.

Like iron is reacts with oxides then its changes iron color. Like that brass converts into colorless.

Blank22 said: (Sep 27, 2015)  
How hard is that?

Chemistry Begineer said: (Sep 28, 2015)  
Different substance have different reactivity, so hydrogen sulphide is it's corroded form. Maybe.

Ssd said: (Sep 28, 2015)  
Brass is a compound of cu and zn.

Ayush said: (Oct 2, 2015)  
What is its equation?

Himani said: (Oct 7, 2015)  
Why we choose hyroden sulphide? I can't understand. Please anybody help me.

Gosego said: (Nov 3, 2015)  
Because hydrogen sulphide is an acid. Hence being corrosive.

Dev said: (Nov 4, 2015)  
Actually, Brass is not a simple metal but an alloy i.e. a mixture of Cu and Zn. Generally sulphur in air is very reactive to copper mixtures. So the answer is B.

Ankit said: (Nov 5, 2015)  
Because brass is react with sulphide then it will corroded.

Shafici said: (Dec 6, 2015)  
We can not choose because it can do it.

So can you do something which you can't do it.

Titli said: (Dec 10, 2015)  
Why answer is B option?

Asawira Emaan Khan said: (Dec 17, 2015)  
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!

David ,Murai said: (Jan 13, 2016)  
What is the disadvantage of nitrogen?

Nandhini said: (Feb 9, 2016)  
Why not carbon-dioxide is correct answer?

Navendu said: (Feb 18, 2016)  
Should it be oxygen?

Angela said: (Feb 20, 2016)  
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.

Ajay K Deshmukh said: (Apr 12, 2016)  
Why brass gets discolored when it reacts hydrogen sulphide?

Xemox said: (May 19, 2016)  
Because when oxygen reacts with hydrogen chloride its get discolored.

Shreya Acharjya said: (Jul 1, 2016)  
But why can't it be nitrogen?

Mccoronnie Delonte said: (Jul 2, 2016)  
I can't understand, I think it's either A or B, I'm not sure about my answer.

Valerie said: (Jul 6, 2016)  
I actually think its A because oxygen usually causes things to rust l8k at the places with a lot of oxygen in the atmosphere.

Dev said: (Jul 9, 2016)  
Because all other options are gas only.

Dev said: (Jul 9, 2016)  
Because Hydrogen Sulphide is an acid. As because of acid it reacts with brass and discolored the brass.

Ismail said: (Jul 16, 2016)  
Its because of the reaction between brass and hydrogen sulphyde. It will be discolour the brass.

Ismail said: (Jul 16, 2016)  
Oxygen can also do this process, but in slowly and in low quantity.

Sch Chowdary said: (Jul 29, 2016)  
@Ismail.

You are right because hydrogen also mixed oxygen and carbon dioxide so hydrogen peroxide.

Nityanand Bharti said: (Aug 8, 2016)  
Because hydrogen sulphaide is an acid.

Patrick said: (Aug 16, 2016)  
Hydro sulphide is a colourless gas when mixed with others.

Anilkumar said: (Aug 17, 2016)  
I think the correct answer is carbon-di-oxide.

Umar Ali said: (Aug 28, 2016)  
If option "b" (Hydrogen Sulphide) is the correct one then please can anybody tell me that, is hydrogen sulphide is present in the air? I think it is not and the correct answer is Co2.

Malaisha said: (Oct 18, 2016)  
No, the correct answer is option A.

Hina Shafiq said: (Oct 18, 2016)  
Yeah, option "b" is correct because brass is a metal and hydrogen sulphide reacts rapidly with metal.

Vinu said: (Oct 29, 2016)  
Can't understand. What's the correct answer.

Remo said: (Nov 1, 2016)  
I think option B is correct because brass is an alloy made of copper and zinc; the proportion of zinc and copper can be varied to create a range of brasses with varying properties.

Ajoy J Tharakan said: (Nov 16, 2016)  
Guys, If it would have been Oxygen, Carbon Dioxide or Nitrogen then you would easily notice the colour change in your brass utensils. That is common sense, also hydrogen sulphide reacts easily with metals like Brass.

Sachin said: (Nov 21, 2016)  
Which of the following gases in air units with many metals?

(A) Hydrogen
(B) Oxygen
(C) Helium
(D) Carbon dioxide

Please tell me the answer.

Jamelia said: (Nov 27, 2016)  
I believe it is option c.

Firoz said: (Nov 28, 2016)  
Oxygen @Sachin.

Lauren said: (Dec 3, 2016)  
All these comments only for one questions.

Jeron said: (Dec 5, 2016)  
No, it is option B because they are asking discoloured one.

Ashritha said: (Dec 13, 2016)  
As per my knowledge, it is option A.

Tushar Kumar said: (Dec 25, 2016)  
It is because of chemical reaction.

Saurabh said: (Jan 4, 2017)  
Why we found a milky colour sample of C.G.C KOD'S drain?

Sonia said: (Jan 7, 2017)  
It is because of chemical reaction.

Ankur said: (Jan 8, 2017)  
This is called Tarnishing. It is a thin layer of corrosion that forms over copper, brass, silver, aluminium, magnesium and other similar metals as their outermost layer undergoes a chemical reaction. Tarnish does not always result from the sole effects of oxygen in the air. For example, silver needs hydrogen sulfide to tarnish, although it may tarnish with oxygen over time. It often appears as a dull, grey or black film or coating over metal. Tarnish is a surface phenomenon that is self-limiting, unlike rust. Only the top few layers of the metal react, and the layer of tarnish seals and protects the underlying layers from reacting the tarnishing.

Nipun said: (Jan 14, 2017)  
According to me, the answer is option A.

Hina said: (Jan 23, 2017)  
Whats the optional element other than H2S?

Himanshu said: (Jan 27, 2017)  
How H2S effect it?

Aditee Agrawal said: (Jan 30, 2017)  
I think because other gases are inert. So, the correct answer is b.

Himanshu said: (Feb 2, 2017)  
This is not a fact @Aditee.

Manvitha Sai said: (Feb 13, 2017)  
I think the correct answer is hydrogen.

K.Manvithasai said: (Feb 13, 2017)  
The correct option is A.

Parikshit said: (Feb 20, 2017)  
I do think so the correct option is A. It can't be B at all. Just pay attention that iron gets rust due to moisture mostly from oxygen.

Shyam said: (Feb 21, 2017)  
The correct option is B. I also agree.

Maimuna said: (Feb 22, 2017)  
Please someone clearly explain the mechanism behind this process, it's very confusing for me.

Dhruv Gaur said: (Feb 28, 2017)  
The correct option is b. I agree.

Ameya B said: (Mar 6, 2017)  
I think its option (A) as the content of hydrogen sulphide in the air is almost 0.

Anupriya said: (Mar 19, 2017)  
I think that option oxygen. As brass gets react with oxygen and get rust.

Anupriya said: (Mar 19, 2017)  
I think the correct option is oxygen. As brass gets react with oxygen and get rust.

Anupriya said: (Mar 19, 2017)  
It may be the chemical reaction.

Rishi said: (Apr 13, 2017)  
According to me, It could be a carbon dioxide.

Ankita said: (Apr 20, 2017)  
I think the correct option is oxygen as brass react with oxygen.

Varsha said: (May 31, 2017)  
Because it is a powerful gas.

Sudha said: (Jun 3, 2017)  
Hydrogen sulphide is a heavy gas, it has property to react with metals like copper, bronze, steel etc. At some conditions (temperature, moisture) brass is a metal (alloy) made of copper and zinc. These two metals are mixed in different proportions. Copper reacts with hydrogen sulphide which makes it corrosive.

Koushik said: (Jun 6, 2017)  
Hydrogen sulphide is a heavy gas, it has property to react with metals like copper, bronze, steel etc. At some conditions (temperature, moisture) brass is a metal (alloy) made of copper and zinc. These two metals are mixed in different proportions. Copper reacts with hydrogen sulphide which makes it corrosive.

Saurabh Agrahari said: (Jun 21, 2017)  
A is a better option because reactive free oxygen species is helpful to discolour the brass because free radical of oxygen may present which is react with brass.

Glory said: (Jul 26, 2017)  
Because it is a powerful gas.

Rohith said: (Aug 12, 2017)  
It is a powerful gas.

Vipin Kumar said: (Aug 21, 2017)  
It oxidises brass that result in change of colour.

Tanav said: (Aug 22, 2017)  
I think answer B is right.

Precious Afriyie said: (Aug 23, 2017)  
The correct answer is B.

Komal said: (Aug 29, 2017)  
I think option B is the correct answer.

Agyare Isaac said: (Aug 31, 2017)  
The right answer is option B. I agree.

Jayanth said: (Sep 2, 2017)  
It is a mixture of cu+zn.

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