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All questions of Introduction to Chemistry for SSS 1 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?

Anshu Anshu answered
Options C is the correct answer because decomposition reaction is a reaction in which a single substance break down into two or more substances.

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.

When Iron nails are added to an aquous 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?

Ishan Choudhury answered
Fe(s) + CuSO4​ ⟶ Cu(s) + FeSO4​
When an iron nail is dipped in copper sulphate solution, a brown coating of copper is formed on the surface of iron and the colour of copper sulphate solution changes from blue to light green. This reaction shows that iron is more reactive than copper as it displaces copper from its solution and iron passes into solution as Fe2+ ions and ferrous sulphate solution is formed.

A strip of copper was placed in a beaker containing zinc sulphate solution. On observing the strip next day, it was noticed that:
  • a)
    The colour of the copper strip changed.
  • b)
    The copper strip remained as it was.
  • c)
    The copper strip became thicker.
  • d)
    The copper strip became thinner.
Correct answer is option 'B'. Can you explain this answer?

Khusboo bhatia answered
A single replacement reaction is one in which a more reactive element displaces a less reactive element from its salt solution.
But copper can not lose electrons easily as compared to zinc and do not result in any reaction.
Thus there will no color change as no chemical reaction take place between the two.

Fe2O3 + 2Al → Al2O3 + 2Fe  This reaction is an example of –
  • a)
    Combination reaction
  • b)
    Double displacement reaction
  • c)
    Decomposition reaction
  • d)
    Displacement reaction
Correct answer is option 'D'. Can you explain this answer?

Amit Kumar answered
Fe2O3 + 2Al → Al2O3 + 2Fe
This reaction is an example of a displacement reaction.
Here, Aluminum is more reactive metal than Fe. Therefore, Al will displace Fe from its oxide.

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.

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 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.

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.

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.

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.
 

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 metal comes below copper in reactivity series ?
  • a)
    Aluminium
  • b)
    Iron
  • c)
    Silver
  • d)
    Zinc
Correct answer is option 'C'. Can you explain this answer?

Krishna Iyer answered
Nature of material of which they are made resistance is depend upon nature of material of which they are made for two wire of same physical dimensions one of the mode of copper and another is silver then reside of silver is much less then resistance of copper

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.

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.

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?

Maheshwar Jain answered
Combination Reaction:
Combination reaction is characterized by the formation of a single product from two or more reactants. This type of reaction involves the coming together of two or more substances to form a single compound.

Key Points:
- In a combination reaction, two or more reactants combine to form a single product.
- The general form of a combination reaction can be represented as: A + B → AB.
- This reaction typically involves the synthesis of a new compound.
- An example of a combination reaction is the formation of water from hydrogen and oxygen: 2H2 + O2 → 2H2O.
In summary, a combination reaction is a type of chemical reaction in which two or more reactants combine to form a single product. This process is characterized by the merging of substances to create a new compound.

Assertion (A): Chemical equations can be made more concise and useful if we use chemical formulae instead of words.
Reason (R): A chemical equation represents a chemical reaction.
  • 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 'B'. Can you explain this answer?

Sandeep Banerjee answered
Assertion and Reason Overview
The Assertion (A) and Reason (R) provided in the question are both true statements about chemical equations. However, it's essential to understand their relationship to determine the correct answer.
Assertion (A) Explanation
- Chemical equations indeed become more concise and useful when expressed using chemical formulae rather than words.
- For example, the reaction of hydrogen and oxygen to form water can be represented as 2H₂ + O₂ → 2H₂O instead of saying "two molecules of hydrogen gas react with one molecule of oxygen gas to produce two molecules of water."
- This conciseness allows for easier interpretation, communication, and comprehension of chemical reactions.
Reason (R) Explanation
- A chemical equation does represent a chemical reaction. It provides a symbolic representation of the reactants and products involved.
- This representation is crucial for understanding the stoichiometry of reactions, predicting the outcomes, and balancing equations.
Relationship Between A and R
- While both statements are true, the reason does not directly explain why the assertion is correct.
- The assertion focuses on the conciseness and usefulness of chemical formulae, while the reason merely states that chemical equations represent reactions without addressing their utility or conciseness.
Conclusion
- Therefore, the correct choice is (b): "If both Assertion and Reason are true but Reason is not the correct explanation of Assertion."
- This choice correctly identifies that although the reason supports the context of chemical equations, it doesn't elucidate why using chemical formulae is preferable over words.

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?

Upsc Toppers answered
  • Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants.

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.

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.

Choose the correctly matched pair.
  • a)
    All of these
  • b)
    Zinc + Hydrochloric acid → Zinc chloride + Hydrogen
  • c)
    Lead nitrate + Potassium iodide → Lead iodide + Potassium nitrate
  • d)
    Magnesium + Nitrogen → Magnesium nitride
Correct answer is option 'A'. Can you explain this answer?

Lakesway Classes answered
  • Option B: (b) Zinc + Hydrochloric acid → Zinc chloride + Hydrogen is correct. The correct reaction is Zinc + Hydrochloric acid → Zinc chloride + Hydrogen gas. Though the products are correct,
  • Option C: (c) Lead nitrate + Potassium iodide → Lead iodide + Potassium nitrate is correct. The actual reaction is Lead nitrate + Potassium iodide → Lead iodide + Potassium nitrate 
  • Option D: (d) Magnesium + Nitrogen → Magnesium nitride is correct. This reaction is discussed in the provided content. The correct reaction would be Magnesium + Nitrogen → Magnesium nitride (Mg3N2)
    so all options are correct so 
    Option (A) is correct

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?

Nandini Bose answered
Understanding the Assertion and Reason
The assertion states that the burning of natural gas is an example of an exothermic reaction. The reason provided explains that exothermic reactions release heat energy along with the formation of products.
Analysis of the Assertion (A)
- The burning of natural gas (primarily methane) involves a chemical reaction with oxygen.
- This reaction produces carbon dioxide and water, releasing energy in the form of heat and light.
- Thus, the assertion is true because burning natural gas indeed qualifies as an exothermic reaction.
Analysis of the Reason (R)
- Exothermic reactions are characterized by the release of heat during the reaction.
- The formation of products in such reactions occurs while energy is released.
- Therefore, the reason is also true as it accurately describes the nature of exothermic reactions.
Connecting the Assertion and Reason
- The reason explains why the assertion is true.
- The release of heat energy during the burning of natural gas is a key characteristic of exothermic reactions.
Conclusion
- Both the assertion and the reason are true.
- The reason is the correct explanation for the assertion.
Thus, the correct answer is option 'C': Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

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?

Nandita Saha answered
Explanation of Combination Reaction
In the reaction given in option (a):

CaO + HO → Ca(OH) + Heat
This is classified as a combination reaction.

What is a Combination Reaction?
- A combination reaction occurs when two or more reactants combine to form a single product.
- In this case, calcium oxide (CaO) and water (HO) combine to form calcium hydroxide (Ca(OH)₂).

Heat Production
- The reaction releases heat, indicating it is exothermic. This is another characteristic of many combination reactions.

Analysis of Other Options

Option B:
- Fe + 4HO → FeO + 4H: This is incorrectly labeled as a decomposition reaction. In reality, it seems to suggest a reaction involving iron and water, but it's not a typical decomposition.

Option C:
- 3Fe + 4HO → FeO + 4H: This is also not a displacement reaction. It’s a misrepresentation of how iron reacts with water.

Option D:
- CO + 2H → CHOH: This is not a displacement reaction either. It’s a synthesis reaction where carbon monoxide and hydrogen combine to form methanol.

Conclusion
- Therefore, option (a) is the only correctly matched pair, as it represents a classic example of a combination reaction, while the others are inaccurately described.

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.

    •  

The word-equation for the reaction of magnesium with oxygen can be written as Magnesium + _____ → Magnesium oxide.
  • a)
    Oxygen
  • b)
    Hydrogen
  • c)
    Nitrogen
  • d)
    Carbon
Correct answer is option 'A'. Can you explain this answer?

Lakesway Classes answered
In the given chemical reaction, magnesium reacts with oxygen to form magnesium oxide. The missing element that reacts with magnesium in this case is oxygen.

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.

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