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All questions of Chemical Reactions for Year 10 Exam

Which of the following is a combination reaction?
  • a)
    CaCO3 → CaO + CO2
  • b)
    H2 + Cl2 → 2HCl
  • c)
    H2CO3 → H2O + CO2
  • d)
    2KClO3 → 2KCl + 3O2
Correct answer is option 'B'. Can you explain this answer?

Roshni chauhan answered
Balanced Equation:
H2 + Cl2 → 2HCl2
The above reaction is an example of combination reaction because two different elements are combining to form a single compound.
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Which of the following is a decomposition reaction?
  • a)
    NaOH + HCl → NaCl + H2O
  • b)
    NH4CNO → H2NCONH2
  • c)
    2KClO3 → 2KCl + 3O2
  • d)
    H2 + I2 → 2HI
Correct answer is option 'C'. Can you explain this answer?

Meera Rana answered
A decomposition reaction occurs when one reactant breaks down into two or more products. Examples of decomposition reactions include the breakdown of hydrogen peroxide to water and oxygen, and the breakdown of water to hydrogen and oxygen.
2KClO3 → 2KCl + 3O2

The reaction C + O2  → CO2 + Heat is a:
  • a)
    Combination reaction
  • b)
    Oxidation reaction
  • c)
    Exothermic reaction
  • d)
    All of the above
Correct answer is option 'D'. Can you explain this answer?

Amit Sharma answered
C + O2  → CO2 + Heat
  • This is a Combination reaction because C and O2 are combining to produce one single compound CO2.
  • This is also an Oxidation reaction because carbon is getting oxidized.
  • This is also an exothermic reaction because in this reaction heat is getting released.
​​​​​​​So Option D is correct

Which one of the following will be required to identify the gas evolved when diluted HCl reacts with zinc metal?
  • a)
    Red litmus solution
  • b)
    Lime water
  • c)
    A burning splinter
  • d)
    Blue litmus solution
Correct answer is option 'C'. Can you explain this answer?

Kiran Mehta answered
A burning splinter since hydrogen gas burns with a pop sound.
Zinc being an active metal readily reacts with hydrochloric acid at room temperature to form soluble zinc chloride and hydrogen.
Zn + 2HCl → ZnCl2 + H2.

Which of the following is a displacement reaction?
  • a)
    CaCO3 → CaO + CO2
  • b)
    CaO + 2HCl → CaCl2 + H2O
  • c)
    Fe + CuSO4 → FeSO4 + Cu
  • d)
    NaOH + HCl → NaCl + H2O
Correct answer is option 'C'. Can you explain this answer?

Gaurav Kumar answered
Fe + CuSo4 → FeSO4 + Cu 
is displacement reaction.
In these reaction iron (Fe) displace copper (Cu) 
Hence, it is a displacement type of reaction.
(a) is a decomposition reaction.
(b) and (d) are neutralisation reactions.

Which of the following metals comes above zinc in reactivity series?
  • a)
    Silver
  • b)
    Copper
  • c)
    Aluminium
  • d)
    Iron
Correct answer is option 'C'. Can you explain this answer?

Karthik murthy answered
Reactivity Series:

The reactivity series is a list of metals arranged in order of their decreasing reactivity. The most reactive metal is placed at the top and the least reactive metal is placed at the bottom of the series.

The reactivity series of metals is as follows:

Potassium > Sodium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > Copper > Silver > Gold

Explanation:

Aluminium is more reactive than zinc and is placed above zinc in the reactivity series. This is because aluminium has a stronger tendency than zinc to lose electrons and form positive ions.

When aluminium is exposed to air, it reacts with oxygen to form a layer of aluminium oxide. This layer of oxide is very thin and is also very stable. It prevents further reaction of aluminium with oxygen and protects the metal from corrosion.

Zinc, on the other hand, reacts with oxygen in the air to form zinc oxide. However, the layer of oxide formed on zinc is not as stable as the layer of oxide formed on aluminium. Therefore, zinc is more susceptible to corrosion than aluminium.

Conclusion:

In conclusion, aluminium is more reactive than zinc and is placed above zinc in the reactivity series. This means that aluminium can displace zinc from its compounds in a chemical reaction, but zinc cannot displace aluminium from its compounds.

The reaction H2 + Cl2 → 2HCl is a –
  • a)
    Decomposition reaction
  • b)
    Combination reaction
  • c)
    Double displacement reaction
  • d)
    Displacement reaction
Correct answer is option 'B'. Can you explain this answer?

Anjana Khatri answered
It is a reaction in which two substances react with each other to make a single substance. Therefore, H2 + CL2 = 2HCL is an COMBINATION REACTION. It is a special case of addition reaction known as synthesis.

In reaction SO2 + 2H2S → 2H2O + 3S, the reducing agent is
  • a)
    SO2
  • b)
    H2S
  • c)
    H2O
  • d)
    S
Correct answer is option 'B'. Can you explain this answer?

Raghav Bansal answered
  • In the reaction SO2 is getting reduced to S as oxygen is being removed.
  • Similarly, H2S is oxidised to S as hydrogen is removed.
  • The species getting oxidised facilitates the reduction process and is the reducing agent.
  • Hence, H2S is the reducing agent and Oxidising agent is SO2.
So, option B is correct

The colour of zinc metal is
  • a)
    reddish-brown
  • b)
    grey 
  • c)
    Blue
  • d)
    silvery-white
Correct answer is option 'D'. Can you explain this answer?

Vikas Kumar answered
The correct option is D
silvery-white
Explanation for correct option
(D) The color of Zinc metal is silvery.
  • An electron gets excited to a higher energy orbital from a lower energy d orbital. The frequency of light absorbed is proportional to the excitation energy.
  • This frequency is usually in the visible range.
  • The color seen corresponds to the complementary color of the light absorbed.
  • Zinc (Zn) is a silvery-white metal.
Hence, option (D) is correct. The color of Zinc metal is silvery.

Which of the following is not an example of chemical change?
  • a)
    rusting of iron
  • b)
    milk changes to curd
  • c)
    digestion of food in our body
  • d)
    changing of water to water vapour
Correct answer is option 'D'. Can you explain this answer?

Amit Sharma answered
The process of changing water vapour into water is called condensation. It is not a chemical reaction.
When milk converts in curd the process is irreversible and a new substance with different properties is formed hence it is an example of a chemical change.
Rusting of iron is also a chemical change.
 

The reaction, Zn + 2HCl → ZnCl2 + H2 is an example of:
  • a)
    Displacement reaction
  • b)
    Combination reaction
  • c)
    Double displacement reaction
  • d)
    Decomposition reaction
Correct answer is option 'A'. Can you explain this answer?

Neha Patel answered
This is a metal/acid reaction if carried out in aqueous solution. 
It is also a displacement reaction where 1 atom of Zinc displaces 2 H+ ions 
and it is a redox reaction as the Zn atom loses electrons (it is OXIDISED) and the 2 H+ ions gain electrons (they are REDUCED) 

What happens when dil hydrochloric acid is added to iron fillings?
  • a)
    Hydrogen gas and Iron chloride are produced
  • b)
    Chlorine gas and Iron hydroxide are produced
  • c)
    NO reaction takes place
  • d)
    Iron salt and water are produced
Correct answer is option 'A'. Can you explain this answer?

Amit Sharma answered
  • Hydrogen gas and iron chloride are produced.
Fe + HCl →  FeCl2  + H2
  • The iron displaces hydrogen from hydrochloric acid to form iron (II) chloride & hydrogen gas. This is a single displacement reaction.
  • Thus the answer is option (A) Hydrogen gas and iron chloride are produced.

An element X on exposure to moist air turns reddish-brown and a new compound Y is formed. The substance X and Y are
  • a)
    X = Fe, Y = Fe2O3
  • b)
    X = Ag, Y = Ag2S
  • c)
    X = Cu, Y = CuO
  • d)
    X = Al, Y = Al2O3
Correct answer is option 'A'. Can you explain this answer?

Suresh Reddy answered
An element X exposure to moist air, forms a reddish brown and a new compound Y is formed. 
Fe + H2O +O2  →  Fe2 O3 
This Fe2O3 is the reddish brown compound which is called rust. 
So , X → Fe 
Y →  Fe2O3
​​​​​​​So Option A is correct

Which of the following statement is incorrect?
  • a)
    In oxidation, oxygen in added to a substance.
  • b)
    In reduction, Hydrogen is added to a substance.
  • c)
    Oxidizing agent is oxidized.
  • d)
    Reducing agent is oxidized
Correct answer is option 'C'. Can you explain this answer?

Nk Classes answered
  • a) In oxidation, oxygen is added to a substance: This is correct. Oxidation involves the addition of oxygen or the loss of electrons.
  • b) In reduction, hydrogen is added to a substance: This is correct. Reduction typically involves the addition of hydrogen or the gain of electrons.
  • c) Oxidizing agent is oxidized: This is incorrect. The oxidizing agent is actually reduced as it gains electrons during the reaction, thereby oxidising the other substance.
  • d) Reducing agent is oxidized: This is correct. The reducing agent loses electrons (is oxidized) while it reduces the other substance by donating electrons.

In reaction SO2 + 2H2S → 2H2O + 3S the reducing agent is –
  • a)
    SO2
  • b)
    H2S
  • c)
    H2O
  • d)
    S
Correct answer is option 'B'. Can you explain this answer?

Navya Patel answered
In the reaction SO2 is reduced to S as oxygen is removed.
H2S is oxidised to S as hydrogen is removed.
The species getting oxidised facilitates the reduction process and is the reducing agent.
Hence, H2S is the reducing agent and Oxidising agent is SO2.

The given reaction indicates that:
Cu + 2AgNO3 → Cu(NO3)2 + 2Ag
  • a)
    Copper is more reactive than silver.
  • b)
    Silver is more reactive than copper.
  • c)
    Both are equally reactive.
  • d)
    None of these
Correct answer is option 'A'. Can you explain this answer?

Malini sharma answered
Explanation:

The given reaction is: Cu + 2AgNO3 → Cu(NO3)2 + 2Ag

This reaction involves the displacement of silver from its compound (AgNO3) by copper. This type of reaction is known as a single displacement reaction or a substitution reaction.

To determine which metal is more reactive, we need to look at the activity series of metals. This series arranges metals in order of their reactivity, with the most reactive metals at the top and the least reactive at the bottom.

Copper is placed below silver in the activity series, which means that silver is more reactive than copper. Therefore, when copper is added to silver nitrate solution, it displaces the silver from its compound and forms copper nitrate. The displaced silver ions combine with copper atoms to form solid silver, which is observed as a brownish precipitate.

Hence, the correct option is A - Copper is more reactive than silver.

Choose the correctly matched pair:
  • a)
    CaO + H₂O → Ca(OH)₂ + Heat - Combination Reaction
  • b)
    Fe + 4H₂O → Fe₃O₄ + 4H₂ - Decomposition Reaction
  • c)
    3Fe + 4H₂O → Fe₃O₄ + 4H₂ - Combination Reaction
  • d)
    CO + 2H₂ → CH₃OH - Displacement Reaction
Correct answer is option 'A'. Can you explain this answer?

Lakesway Classes answered
  • Option A: CaO + H₂O → Ca(OH)₂ + Heat - This is correctly matched as a Combination Reaction. In this reaction, calcium oxide (CaO) reacts with water (H₂O) to form calcium hydroxide (Ca(OH)₂) and releases heat. This is a classic example of a combination reaction where two or more substances combine to form a single product.
  • Option B: Fe + 4H₂O → Fe₃O₄ + 4H₂ - This reaction is incorrectly labeled as a Decomposition Reaction. It is actually a redox reaction involving the oxidation of iron and the reduction of water.
  • Option C: 3Fe + 4H₂O → Fe₃O₄ + 4H₂ - This is also incorrectly labeled. Although there is a combination of elements involved, it is best described as a redox reaction rather than a simple Decomposition reaction.
  • Option D: CO + 2H₂ → CH₃OH - This is incorrectly matched as a Displacement Reaction. It is actually a synthesis reaction where carbon monoxide (CO) and hydrogen (H₂) combine to form methanol (CH₃OH).

Which of the following is a balanced chemical equation?
  • a)
    H₂ + O₂ → H₂O
  • b)
    2H₂ + O₂ → H₂O
  • c)
    H₂ + 2O₂ → H₂O
  • d)
     
    2H₂ + O₂ → 2H₂O
Correct answer is option 'D'. Can you explain this answer?

Lakesway Classes answered
2H2 + O2 → 2H2O
The balanced chemical equation is:

  • 2 molecules of hydrogen gas (H2) react with 1 molecule of oxygen gas (O2).

  • This produces 2 molecules of water (H2O).

  • Each side of the equation has 4 hydrogen atoms and 2 oxygen atoms, ensuring mass conservation.

    •  

What type of reaction is characterized by the formation of a single product from two or more reactants?
  • a)
    Combination Reaction
  • b)
    Decomposition Reaction
  • c)
    Displacement Reaction
  • d)
    Double Displacement Reaction
Correct answer is option 'A'. Can you explain this answer?

Lakesway Classes answered
In a combination reaction, multiple reactants combine to form a single product. An example is the reaction between calcium oxide and water to produce calcium hydroxide. This type of reaction involves the synthesis of a new compound from the combining of elements or compounds.

Choose the correctly matched pair.
  • a)
    Burning of coal - C(s) + O2(g) → CO(g)
  • b)
    Formation of water - 2H2(g) + O2(g) → 2H2O2(l)
  • c)
    Respiration - C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O2(l) + energy
  • d)
    Whitewashing reaction - Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
Correct answer is option 'D'. Can you explain this answer?

Lakesway Classes answered
  • Let's analyze each option to determine the correctly matched pair:
  • Option A: (a) Burning of coal - C(s) + O2(g) → CO2(g)
  • This is a correct chemical equation for the burning of coal, which is a combination reaction. However, let's verify the other options before concluding.
  • Option B: (b) Formation of water - 2H2(g) + O2(g) → 2H2O(l)
  • This is also a correct chemical equation for the formation of water from hydrogen and oxygen, which is another example of a combination reaction. We need to check the remaining options as well.
  • Option C: (c) Respiration - C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + energy
  • This equation correctly represents the process of respiration, an exothermic reaction where glucose reacts with oxygen to produce carbon dioxide, water, and energy.
  • Option D: (d) Whitewashing reaction - Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
  • This is the correct chemical equation for the whitewashing reaction. When calcium hydroxide reacts with carbon dioxide, it forms calcium carbonate (which gives a shiny finish on walls) and water.
  • All options are correctly matched pairs, but the question asks for one correctly matched pair. Therefore, Option D is chosen as it represents a familiar and specific application that students are likely to recognize easily.

Which form of energy is responsible for the decomposition reactions ?
  • a)
    Heat
  • b)
    All of these
  • c)
    Electricity
  • d)
    light
Correct answer is option 'B'. Can you explain this answer?

Sahana Menon answered
Decomposition reactions and energy:
There are various forms of energy that can drive decomposition reactions, breaking down compounds into simpler substances.

All of these:
- Heat: Many decomposition reactions are initiated by heating the compound, which provides the necessary energy to break bonds and start the decomposition process. This is a common method used in industries and laboratories.
- Electricity: In some cases, passing an electric current through a compound can trigger decomposition reactions. This is known as electrolysis and is commonly used in processes like electroplating and water electrolysis.
- Light: Certain compounds can undergo decomposition reactions when exposed to light, especially ultraviolet light. This phenomenon is known as photolysis and is utilized in various chemical reactions.
Therefore, all of these forms of energy - heat, electricity, and light - can be responsible for driving decomposition reactions. Each form of energy provides the necessary activation energy to break the existing bonds in a compound, leading to its decomposition into simpler substances.

Assertion (A): The iron nail becomes brownish in color and the blue color of copper sulfate solution fades.
Reason (R): In the reaction Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s), iron displaces copper in the copper sulfate solution.
  • a)
    If both Assertion and Reason are true and Reason is the correct explanation of Assertion
  • b)
    If both Assertion and Reason are true but Reason is not the correct explanation of Assertion
  • c)
    If Assertion is true but Reason is false
  • d)
    If both Assertion and Reason are false
Correct answer is option 'A'. Can you explain this answer?

Lakesway Classes answered
  • The Assertion is true as the iron nail indeed becomes brownish and the blue color of the copper sulfate solution fades due to the displacement reaction described.
  • The Reason is also true as iron displaces copper from the copper sulfate solution.
  • The Reason is the correct explanation of the Assertion because the observed color changes are a direct result of the displacement reaction where iron replaces copper in the solution.

Identify the substances that are oxidised and the substances that are reduced in the following reaction.
Fe2O3 + 2Al → Al2O3 + 2Fe
  • a)
    Fe2O3
  • b)
    Al
  • c)
    Fe
  • d)
    Both A and B
Correct answer is option 'D'. Can you explain this answer?

Kds Coaching answered
To identify the substances that are oxidized and reduced in the given reaction:
Reaction: Fe2O3 + 2Al → Al2O3 + 2Fe
  1. Oxidation involves the loss of electrons.
  2. Reduction involves the gain of electrons.
  • Iron (Fe) in Fe₂O₃:
    • In Fe₂O₃, iron is in the +3 oxidation state.
    • In elemental Fe, the oxidation state is 0.
    • Thus, Fe is reduced from +3 to 0.
  • Aluminum (Al):
    • In elemental Al, the oxidation state is 0.
    • In Al₂O₃, aluminum is in the +3 oxidation state.
    • Thus, Al is oxidized from 0 to +3.
Substances:
  • Substance reduced: Fe₂O₃ (iron is reduced to Fe).
  • Substance oxidized: Al (aluminum is oxidized to Al₂O₃).
Correct Answer: (d) Both A and B
Explanation: Fe₂O₃ is reduced, and Al is oxidized.

What is the substance gaining oxygen and being oxidized during the described reaction?
  • a)
    Cu
  • b)
    O
  • c)
    CuO
  • d)
    Not a redox reaction 
Correct answer is option 'A'. Can you explain this answer?

Arnav raman answered
Understanding the Reaction
The reaction given is:
2Cu(s) + O2(g) → 2CuO(s)
This equation describes a chemical reaction where copper (Cu) reacts with oxygen (O2) to form copper(II) oxide (CuO).
What is Oxidation?
In chemistry, oxidation refers to the process where a substance loses electrons or gains oxygen.
Identifying the Oxidized Substance
- In this reaction, copper (Cu) is the substance that is oxidized.
- Copper reacts with oxygen, and during this process, copper loses electrons and gains oxygen to form CuO.
Oxidation Process
- Copper (Cu) goes from an elemental state (0 oxidation state) to a compound state (oxidation state +2 in CuO).
- By gaining oxygen, Cu is effectively losing electrons, which is the hallmark of oxidation.
Conclusion
- Therefore, the correct answer is option 'A', which indicates that copper (Cu) is the substance that is being oxidized in this reaction.
- Oxygen (O2) is actually being reduced in this process, as it gains electrons by reacting with copper.
In summary, the reaction showcases a redox process where copper is oxidized and oxygen is reduced, clearly identifying copper as the substance that gains oxygen and undergoes oxidation.

Assertion (A): Burning of natural gas is an example of an exothermic reaction.
Reason (R): Exothermic reactions release heat energy along with the formation of products.
  • a)
    If Assertion is true but Reason is false 
  • b)
    If both Assertion and Reason are true but Reason is not the correct explanation of Assertion
  • c)
    If both Assertion and Reason are true and Reason is the correct explanation of Assertion
  • d)
    If both Assertion and Reason are false
Correct answer is option 'C'. Can you explain this answer?

Kamna Science Academy answered
Let's analyze the statements:
Assertion (A): Burning of natural gas is an example of an exothermic reaction.
  • This is true because burning natural gas (methane, CH4) releases heat energy.
Reason (R): Exothermic reactions release heat energy along with the formation of products.
  • This is also true because exothermic reactions are characterized by the release of heat energy during the reaction process.
Since both statements are true and the Reason correctly explains the Assertion: If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

What is a reduction reaction?
  • a)
    addition of hydrogen to a substance
  • b)
    addition of oxygen to a substance
  • c)
    removal of hydrogen from a substance 
  • d)
    none of the above 
Correct answer is option 'A'. Can you explain this answer?

Kds Coaching answered
In terms of hydrogen and oxygen:
Addition of hydrogen to a substance: Reduction
Removal of oxygen from a substance: Reduction
Therefore, option A, "addition of hydrogen to a substance," correctly defines a reduction reaction.

Why does an iron nail become brownish in color and the blue color of copper sulfate solution fades?
  • a)
    Due to a chemical reaction with air
  • b)
    Because of a change in temperature
  • c)
    As a result of a displacement reaction
  • d)
    Through a physical reaction with water
Correct answer is option 'C'. Can you explain this answer?

Divey Sethi answered
  • When an iron nail is immersed in a copper sulfate solution, a displacement reaction occurs.
  • In this reaction, iron displaces copper from copper sulfate solution, leading to the formation of iron sulfate and metallic copper.
  • This explains why the iron nail turns brownish and the blue color of the copper sulfate solution fades, showcasing a classic example of a displacement reaction.

A chemical equation is said to be balanced if number of
  • a)
    Compounds are same in both sides
  • b)
    Molecules are same in both sides
  • c)
    Number of atoms is same in both sides
  • d)
    Number of electrons are same in both sides
Correct answer is option 'C'. Can you explain this answer?

Debolina Nair answered
Balanced chemical equation: A balanced equation is a chemical equation in which number of atoms of each element is equal on both sides of the equation i.e number of atoms of an element on reactant side = number of atoms of that element on the product side.

Identify the reaction: 
AgNO3(aq) + KCl(aq) → AgCl↓ + KNO3(aq)
  • a)
    Combination reaction
  • b)
    Decomposition reaction
  • c)
    Precipitation reaction
  • d)
    None of these
Correct answer is option 'C'. Can you explain this answer?

Tushar Kumar answered
Understanding the Reaction
The reaction in question is:
AgNO3(aq) + KCl(aq) → AgCl↓ + KNO3(aq)
This equation represents the interaction of silver nitrate and potassium chloride in aqueous solution.
What is a Precipitation Reaction?
- A precipitation reaction occurs when two soluble salts react in solution to form an insoluble product, known as a precipitate.
- In this case, AgCl is the precipitate, which is insoluble in water, and it forms as a solid that can be seen separating from the solution.
Identifying the Components
- Reactants:
- AgNO3 (silver nitrate) and KCl (potassium chloride) are both soluble in water and dissociate into their respective ions.
- Products:
- AgCl (silver chloride) is the insoluble precipitate that forms and KNO3 (potassium nitrate) remains soluble.
Why is it a Precipitation Reaction?
- The formation of AgCl (a solid) from the reaction indicates that a new substance is created that cannot stay dissolved in the solution.
- The downward arrow (↓) next to AgCl signifies that it is a precipitate.
Conclusion
In summary, the reaction between AgNO3 and KCl is classified as a precipitation reaction (option C) because it results in the formation of an insoluble solid (AgCl) from the interaction of two aqueous solutions. This is a key concept in understanding chemical reactions and their classifications in chemistry.

What is a oxidation reaction?
  • a)
    addition of hydrogen to a substance
  • b)
    addition of oxygen to a substance
  • c)
    removal of oxygen from a substance 
  • d)
    none of the above 
Correct answer is option 'B'. Can you explain this answer?

Kds Coaching answered
In terms of hydrogen and oxygen:
Addition of oxygen to a substance: Oxidation
Removal of hydrogen from a substance: Oxidation
Therefore, correct answer is option (b)

When Iron nails are added to an aqueous solution of copper sulphate, a chemical change occurs, which of the following is NOT true about this reaction?
  • a)
    Blue colour of the solution fades.
  • b)
    Iron nails become brownish in colour.
  • c)
    It is a displacement reaction.
  • d)
    Blue colour of the solution does not  fades.
Correct answer is option 'D'. Can you explain this answer?

Kds Coaching answered
Fe(s) + CuSO4​ ⟶ Cu(s) + FeSO4​
Out of the listed options, the statement that is NOT true about the reaction between iron nails and copper sulfate solution is:
4. Blue colour of the solution does not fade.
Here's why the other statements are true:
  1. Blue colour of the solution fades:
    The blue color of the copper sulfate solution comes from copper ions (Cu2+). When iron nails are added, iron (Fe) displaces copper from the solution (displacement reaction). This removes copper ions and leads to the fading of the blue color.
  2. Iron nails become brownish in colour: As iron displaces copper, copper ions are deposited on the iron nails. This gives the iron nails a brownish color due to the presence of copper metal.
  3. It is a displacement reaction: Iron (more reactive) displaces copper (less reactive) from its copper sulfate solution. This is a classic example of a single displacement reaction.
Therefore, the correct answer is 4. Blue colour of the solution does not fade.

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