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All questions of Chemical Reactions for Grade 9 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.

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.
 

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

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.

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.

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.

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.

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.

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.

Chapter doubts & questions for Chemical Reactions - Biology 2025 is part of Grade 9 exam preparation. The chapters have been prepared according to the Grade 9 exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for Grade 9 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.

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