Chemical Reaction MCQ

Chemical Reaction MCQ

Q. CO2 when passed in excess, in lime water turns colourless again because of:

a) Calcium Carbonate

b) Calcium bicarbonate

c) Calcium Chloride

d) Copper Carbonate

Ans: b) Calcium bicarbonate


  • Calcium hydroxide is sparingly soluble in water producing an alkaline solution known as limewater.
  • Calcium Carbonate is a chemical compound found commonly in rocks as minerals and is the main component of pearls and the shells of marine organisms, eggs, etc.
  • When carbon dioxide gas is passed through or over limewater, it turns milky due to the formation of calcium carbonate.
  • However, when an excess of CO2 ​is passed through this solution, the milkiness disappears. This is due to the formation of calcium bicarbonate which is colorless and soluble in water.

Q. Chemical formula of plaster of paris:

a) CaSO4

b) CaSO4.2H2O

c) CaSO4.1/2 H2O

d) CaSO4.H2O

Ans: c) CaSO4.1/2 H2O


  • Plaster of Paris (POP) is a quick-setting gypsum plaster consisting of a fine white powder (calcium sulfate hemihydrate), which hardens when moistened and allowed to dry.
  • It is also known as the Plaster of Paris because for the preparation of POP, the abundant gypsum was first found near the capital city of France i.e. Paris.
  • The chemical formula of the Plaster of Paris is CaSO4.12 H2O. Therefore option 3 is correct.
  • Application of Plaster of Paris is as follows
    1. It is used as a building material as a protective coating on walls and ceilings.
    2. It is used as a moulding and vesting agent for decorative elements.
    3. It is also used for aesthetic touch to the construction elements.
    4. It is also used as plaster in orthopaedics and as a filling material by dentists, etc.
  • Gypsum is an ore of Calcium (Ca). The chemical formula of Gypsum is CaSO4. 2H2O.
  • Gypsum is mainly used as a fertilizer, as the main constituent in plaster, chalk, etc.
  • The plaster of Paris on mixing with water produces gypsum.
  • Calcium Sulphate Hemihydrate (CaSO4·1/2 H2O) on hydration leads to the crystallization of gypsum calcium sulphate dihydrate (CaSO4·2H2O).

Q. Potassium permanganate is used to purify water as its is

a) sterilizing

b) oxidizing

c) reducing

d) leaching

Ans: b) oxidizing

  • Potassium permanganate (KMnO4) is a strong oxidising agent that oxidizes dissolved impurities from water such as iron, manganese, and hydrogen sulphide (H2S) by converting them into solid particles.
  • These impurities are then filtered out of the water.
  • It is a salt consisting of K⁺ and MnO− 4 ions.
  • It is a strong oxidizing agent.
  • It is used as a medication for cleaning wounds and dermatitis.

Q. Bleaching action of chlorine is by

a) decomposition

b) hydrolysis

c) reduction

d) oxidation

Ans: d) oxidation

Chemical Reaction MCQKey Points

  • The bleaching action of chlorine is an oxidation reaction.
  • It requires moisture for its bleaching action. Chlorine reacts with water to form hydrochloric and hypochlorous acids.
    • Cl2 + H2O ——→ HCl + HClO
  • Hypochlorous acid is unstable, and it easily separates to form nascent oxygen.
    • HClO ——→ HCl + [O]
  • Nascent oxygen is the most powerful oxidising agent. Its formation is responsible for the bleaching nature of chlorine in the presence of moisture.

Q. What will be formed by burning hydrogen?

a) Oxygen

b) Ash

c) Soil

d) Water

Ans: d) Water

The correct answer is water.

  • Burning hydrogen in pure oxygen just produces H2O.
  • However, hydrogen would normally be burnt in air and some of the ferociously active oxygen atoms combine with nitrogen in the air to form NO x.
  • There are no carbon atoms for the oxygen atoms to combine with, so a higher proportion combine with nitrogen from the air to form NO x.

Q. Which chemical is widely used to unclog drains and sinks?

a) Sodium Chloride

b) Nitrogen Hydroxide

c) Hydrogen Peroxide

d) Sodium Hydroxide

Ans: d) Sodium Hydroxide

The correct answer is Sodium Hydroxide.

  • Sodium hydroxide is a chemical compound also known as caustic soda.
  • Sodium hydroxide is basic in nature.
  • The chemical formula of Sodium hydroxide is NaOH.
  • Sodium Hydroxide is widely used to unclog drains and sinks.
  • It is frequently used as an industrial cleaning agent.
  • When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide.
  • Sodium hydroxide is mainly used in:
    • The manufacture of pulp and paper.
    • Textile industry.
    • Drinking water industry.
    • Manufacture of fabric, plastic wrap, and soap.

Q. Which of the following compound is responsible for tarnishing of silver?

  1. Ag2O
  2. Ag2CO3
  3. Ag2S
  4. AgCN

Ans: c: Ag2S


  • Silver article turns black when kept in the air because silver article reacts with sulphur compounds such as hydrogen sulphide (H2​S) present in air.

Ag + H2​S → Ag2​S + H2​

  •  The phenomenon is called corrosion. For silver particularly, it is called tarnishing of silver.
  • Silver sulphide (Ag2​S) is the black substance formed.

So, Ag2​S (Silver sulphide) compound is responsible for tarnishing of silver.

Which process takes place when we heat a solution of alum and then let the filtrate cool?

  1. Sublimation
  2. Crystallisation
  3. Magnetic separation
  4. None of these

Answer (Detailed Solution Below)

Option 2 : Crystallisation

Chemical Reaction MCQ Question 9 Detailed Solution


  • If we observe our surroundings, we will see that there is always some transformation occurring, like burning of coal, the formation of clouds, yellowing of leaves, etc. These are called changes.
  • Changes, based on their nature can be classified into two types: Physical and Chemical.
  • A Comparision between chemical and physical changes is as follows:
Chemical changePhysical Change
It involves the formation of completely new products.No new products are formed in physical change.
There is a change in heat, color, etc.Change in only the state of matter occurs.
Cannot be reversed easily, like the burning of wood.Can be reversed easily, like boiling of water.
  • Crystallization:
    • Crystallization is an example of physical change.
    • It involves the separation of solid-liquid, which involves the transfer of solute to the pure solid crystalline phase from the liquid solution.
  • Sublimation: 
    • Sublimation is the transition from the solid phase to the gas on the heating phase without passing through an intermediate liquid phase.
    • After the solid is turned into vapors, it can turn back to solid on cooling


  • We prepare a solution of potash alum by dissolving some alum in water.
  • To dissolve it completely, we heat the solution.
  • After complete dissolution, we filter the solution and let the filtrate cool down.
  • If a crystal of solid alum is hung by a thread in the solution, crystals of alum will start growing on it after some time.
  • If we can keep it for few days, the crystal will become bigger in size.
  • The solute particles of alum transfer to the crystal form on cooling.
  • Thus, the process of crystallization takes place.

Hence, when we heat a solution of alum and then let the filtrate cool crystallization occurs.

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In the presence of oxygen, glucose does NOT break down into which among the following?

  1. Carbondioxide
  2. Alcohol
  3. Water
  4. Energy

Answer (Detailed Solution Below)

Option 2 : Alcohol

Chemical Reaction MCQ Question 10 Detailed Solution

The correct answer is Alcohol.

Chemical Reaction MCQ
  • The process of breakdown of food in the cell with the release of energy is called cellular respiration.
  • In the cell, the food (glucose) is broken down into carbon dioxide and water using oxygen.
  • When the breakdown of glucose occurs with the use of oxygen it is called aerobic respiration.
  • When the breakdown of glucose occurs without the use of oxygen it is called anaerobic respiration.
  • Breakdown of food releases energy.
  • In the absence of oxygen, glucose breaks down into alcohol, carbon dioxide, and energy.
  • In the presence of oxygen, glucose breaks down into the water, carbon dioxide, and energy.
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If dilute sulfuric acid is added to granular zinc, which of the following gases will form?

  1. Sulphur dioxide
  2. Oxygen
  3. Hydrogen sulfide
  4. Hydrogen

Answer (Detailed Solution Below)

Option 4 : Hydrogen

Chemical Reaction MCQ Question 11 Detailed Solution

The correct answer is Hydrogen.

Chemical Reaction MCQKey Points

  • When dilute sulphuric acid is poured on zinc granules, then zinc being more reactive than hydrogen displaces it from the acid and forms zinc sulphate and hydrogen gas. 
    • Zn + H2SO4 → ZnSO4 + H2.
  • Hydrogen is a combustible gas and burns with a popping sound.
  • This can be observed when a match stick that is burnt is bought ear to the test tube.

Additional Information

  • Hydrogen is the chemical element with the symbol H and atomic number 1. 
  • Hydrogen is the lightest element in the periodic table.
  • Hydrogen is the most abundant chemical substance in the universe, constituting roughly 75% of all baryonic mass.
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Substances that decrease the activity of a catalyst are known as _____________.

  1. controllers
  2. promoters
  3. poisons
  4. initiators

Answer (Detailed Solution Below)

Option 3 : poisons

Chemical Reaction MCQ Question 12 Detailed Solution

The correct answer is poisons.

  • Catalytic poisons are those substances that themselves are not catalysts but whose presence decreases the activity of the catalyst.
  • This occurs due to preferential adsorption of poison on the surface of the catalyst.
  • They are also known as anti catalysts or catalyst inhibitors.


  • It is a substance that increases the rate of a reaction without taking a direct part in the reaction.
  • Catalysts do not undergo chemical change in themselves.
  • When we need to control the rate of reaction which has increased due to the addition of a catalyst, catalytic poisons are added.

Chemical Reaction MCQAdditional Information


  • It is a substance added to a solid catalyst to improve its performance in a chemical reaction.
  • The promoter itself has little or no catalytic effect. 


  • Initiators are substances that help to initiate (start) a chemical reaction.


  • Controllers are used for controlling the rate of a chemical reaction.
  • They can be mechanical, thermal, or chemical in nature.
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Which one of the following metals do not react with cold as well as hot water?

  1. Na
  2. Fe
  3. Mg
  4. Ca

Answer (Detailed Solution Below)

Option 2 : Fe

Chemical Reaction MCQ Question 13 Detailed Solution

The correct answer is Fe.

Chemical Reaction MCQKey Points 

  • Metals like iron(Fe), aluminium(Al), and zinc(Zn) do not react with cold as well as hot water.
  • Metals like iron(Fe), aluminium(Al), and zinc(Zn) react with steam to form the metal oxide and hydrogen.
  • Reaction of aluminium(Al) with steam:
    • 2Al(s) + 3H2O(g) → Al2O3(s) + 3H2(g).
  • Reaction of iron(Fe) with steam:
    • 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g).

Chemical Reaction MCQAdditional Information 

  • The calcium(Ca) reacts less violently with water.
    • Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g).
    • Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal.
  • Metals like potassium(K) and sodium(Na) react violently with cold water.
    • The reaction is violent and exothermic.
    • The evolved hydrogen immediately catches fire.
  • Magnesium does not react with cold water.
    • Magnesium reacts with hot water to form magnesium hydroxide and hydrogen.
    • Magnesium starts floating due to the bubbles of hydrogen gas sticking to its surface.
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Which type of reaction takes place when we dissolve ammonium nitrate with water?

  1. Endothermic 
  2. Exothermic
  3. Explosive
  4. None

Answer (Detailed Solution Below)

Option 1 : Endothermic 

Chemical Reaction MCQ Question 14 Detailed Solution

The correct answer is Endothermic.Chemical Reaction MCQKey Points

  • Ammonium nitrate (NH4NO3) segregates into the ammonium cation (NH4+) and the nitrate anion (NO3) when dissolved in water.
  • These ions form ammonium hydroxide (NH4OH) and nitric acid (HNO3respectively by reacting with the OH and H+ ions in water.
  • This reaction is endothermic in nature since it cools the surroundings by absorbing heat from them.

Chemical Reaction MCQImportant Points

  • In endothermic reactions, the reactants absorb heat energy from the surroundings to form products.
  • These reactions lower the temperature of their surrounding area, thereby creating a cooling effect.
  • Example:- Melting ice cubes, melting solid salts, evaporating liquid water.

Chemical Reaction MCQAdditional Information

  • Exothermic reactions are reactions that release energy into the environment in the form of heat.
  • Example- Rusting of iron, and freezing of water.
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Food containing oil and fat, when kept for a longer time, causes a change in its taste and smell due to the process of __________.

  1. decomposition
  2. fermentation
  3. rancidity
  4. substitution

Answer (Detailed Solution Below)

Option 3 : rancidity

Chemical Reaction MCQ Question 15 Detailed Solution

The correct answer is rancidity.

Chemical Reaction MCQ​ 

  • Food containing oil and fat, when kept for a longer time, causes a change in its taste and smell due to the process called rancidity.
    • If there is a change in smell, taste, and color the substance is said to be rancid.
    • Elimination of the oxygen content inside a container is the best way to prevent rancidity.
    • Rancidity can be avoided by keeping food in airtight containers.
    • Airtight containers help to slow down oxidation.


  • ​Decomposition is the process of breaking down dead organic substances into simpler organic or inorganic matter.
  • Fermentation is a metabolic process that makes chemical changes in organic substrates with the help of enzymes.
  • A substitution reaction is a chemical reaction in which one functional group in a chemical compound is replaced by another functional group.
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Burning of candle is which kind of reaction?

  1. Synthesis Reaction
  2. Exothermic Reaction
  3. Endothermic Reaction
  4. Photochemical Reaction

Answer (Detailed Solution Below)

Option 2 : Exothermic Reaction

Chemical Reaction MCQ Question 16 Detailed Solution

The correct answer is  Exothermic Reaction.

  • An exothermic reaction is a chemical reaction that releases energy in the form of light or heat. The burning of the candle is an exothermic reaction.
  • Endothermic reactions – Heat is absorbed, like the Photosynthesis process.
  • When Candle burns both physical and chemical changes takes place
  • Chemical reactions can be classified as five basic types:
    • Combination Reactions – a reaction in which two or more substances combine to form a single new substance.
    • Decomposition Reactions –  a reaction in which a compound breaks down into two or more than two simpler substances.
    • Single-Replacement Reactions – a reaction in which one element replaces a similar element in a compound
    • Double-Replacement Reactions – a reaction in which the positive and negative ions of two ionic compounds exchange places to form two new compounds.

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In which process is a protective zinc coating applied on iron to prevent it from rusting?

  1. Galvanisation 
  2. Annealing
  3. Smelting
  4. Welding

Answer (Detailed Solution Below)

Option 1 : Galvanisation 

Chemical Reaction MCQ Question 17 Detailed Solution

The correct answer is ” Galvanization “.

Chemical Reaction MCQKey Points

  • Galvanization is the process of applying a coating of zinc to steel or iron. 
  • This is done to protect steel and iron from the process of rusting.
  • The most common method of galvanization is ” hot-dip-galvanization”.
  • In this method, parts are submerged in a bath of molten hot zinc.

Important Points

  • Annealing is a heat treatment process used mostly to increase the ductility and reduce the hardness of a material.
  • Smelting is a form of extractive metallurgy to produce a metal from its ore.
  • Welding is a fabrication process whereby two or more parts are fused together by means of heat, pressure or both forming a join as the parts cool. 

​​Chemical Reaction MCQAdditional Information

  • When zinc is coated on iron or steel,  it protects corrosive substances from reaching the underlying steel or iron. 
  • The electroplating such as chromate conversion coating is applied to provide further surface passivation to the substrate material.
  • The hot-dipping method is not applicable to the materials that are constantly exposed to acid and acid rains.
  • It is also not applicable to bolts and nuts.
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Identity the type of chemical reaction in the equation – AgNO+ NaCl → AgCl + NaNO?

  1. Neutralization reaction
  2. Precipitation reaction
  3. Synthesis reaction
  4. Decomposition reaction

Answer (Detailed Solution Below)

Option 2 : Precipitation reaction

Chemical Reaction MCQ Question 18 Detailed Solution

The correct answer is Option(2).i.e.Precipitation reaction.


Chemical Reactions:

  • A process in which one or more compounds are formed as products completely different from the reacting substances is known as a chemical reaction.
  • There is generally a change in heat, color, or appearance when a chemical reaction takes place.
  • The evolution of gas may also occur.
  • A chemical reaction may be reversible or irreversible in nature.
  • Chemical changes occur in chemical reactions.

Types of Chemical Reactions-

Different types of reactions are

  • Combustion reaction
  • Decomposition reaction
  • Neutralization reaction
  • Precipitation or Double-Displacement Reaction


  • Precipitation reactions refer to the formation of insoluble salt when two solutions containing soluble salts are mixed. The insoluble salt that comes out of the solution is known as a precipitate, hence the name of the reaction.
  • Precipitation reactions can help to determine the identity of different ions in the solution.
  • NaCl + AgNO3 ​→ AgCl + NaNO3​

Mol :     1 mol     1 mol        1 mol      1 mol

Mass:   58.5 g     170 g      143.5 g    85 g

  • In the reaction above, AgCl is formed as a precipitate.
  • Hence. the reaction Sodium chloride + silver nitrate → silver chloride + sodium nitrate is a precipitation reaction.

Additional Information

Types of Chemical Reactions-The The basis for different types of reactions is the product formed, the changes that occur, the reactants involved, and so on. Different types of reactions are

  • Combustion reaction
  • Decomposition reaction
  • Neutralization reaction
  • Precipitation or Double-Displacement Reaction

Combustion Reaction

  • It is a reaction with a combustible material with an oxidizer to give an oxidized product.
  • An oxidizer is a chemical a fuel requires to burn, generally oxygen.
  • For an example of the combustion of magnesium metal.2Mg + O2→2MgO + Heat Here, 2 magnesium atoms react with a molecule of oxygen-producing 2 molecules of the compound magnesium oxide-releasing some heat in the process.

Decomposition Reaction

  • It is a reaction in which a single component breaks down into multiple products.
  • Certain changes in energy in the environment have to be made like heat, light, or electricity breaking bonds of the compound. for example of the decomposition of calcium carbonate giving out CaO (Quick Lime) which is a major component of cement. CaCO3(s)→CaO(s)+CO2(g) Here, the compound Calcium carbonate when heated breaks down into Calcium Oxide and Carbon Dioxide.

Neutralization Reaction

  • It is basically the reaction between an acid and a base giving salt and water as the products.
  • The water molecule formed is by the combination of OH- ions and H+ ions. The overall pH of the products when a strong acid and a strong base undergo a neutralization reaction will be 7.
  • Consider the example of the neutralization reaction between Hydrochloric acid and Sodium Hydroxide giving out sodium chloride(Common Salt) and water. HCl + NaOH → NaCl + H2O Here, an acid and a base, Hydrochloric acid and Sodium Hydroxide react in a neutralization reaction to produce Sodium Chloride(Common Salt) and Water as the by-products.

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Iron rusts because of ______ reaction.

  1. Oxidation 
  2. Reduction 
  3. Corrosion 
  4. Redox 

Answer (Detailed Solution Below)

Option 4 : Redox 

Chemical Reaction MCQ Question 19 Detailed Solution


Chemical Reaction MCQConfusion Points

  • During rusting, iron combines with oxygen in the presence of water. This is an oxidation reaction where oxygen acts as an oxidizing agent.
  • Since oxygen also combines with the metal iron, this is a reduction reaction, where the metal iron acts as a reducing agent.
  • So here both oxidation and reduction process is taking place. This combination of these processes is a redox reaction. So the correct answer is the redox reaction. 

Key Points

Rusting of iron is an example of a Redox reaction.

  • Redox reaction = Oxidation-Reduction reaction. In this reaction, an oxidation number of a molecule, atom, or ion changes either by gaining or losing an electron. 
  • The substance which gets reduced in a chemical reaction is known as the oxidizing agent and a substance that gets oxidized in a chemical reaction is known as the reducing agent.
  • Rusting is the corrosion of iron. Iron forms red-brown hydrated metal oxide (rust) in the presence of water and air. 
  • Iron is oxidized to Fe2+ and oxygen is reduced to water. Rust keeps on forming due to the subsequent oxidation of Fe2+ by atmospheric oxygen.
  • Therefore, we can say rusting is a redox reaction because oxygen acts as an oxidising agent, and iron acts as a reducing agent.

Rusting of Iron takes place: Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.

Fe + O2  → Fe2O3 (Iron (III)oxide)

Chemical Reaction MCQImportant Points

Oxidation and Reduction:

  • Rusting is an oxidation reaction. The iron reacts with water and oxygen to form hydrated iron(III) oxide, which we see as rustIron and steel rust when they come into contact with water and oxygen – both are needed for rusting to occur.
  • When acidic substances (including water) come in contact with metals, such as iron and/or steel, rust begins to form. Rust is the result of corroding steel after the iron (Fe) particles have been exposed to oxygen and moisture (e.g., humidity, vapor, immersion).
  • The addition of oxygen to a substance and the removal of hydrogen from a substance is called oxidation.
  • The addition of Hydrogen in a substance and the removal of oxygen from a substance is called reduction.

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The process of rusting of iron is called _____?

  1. Reduction
  2. Galvanization
  3. Absorption
  4. Corrosion

Answer (Detailed Solution Below)

Option 4 : Corrosion

Chemical Reaction MCQ Question 20 Detailed Solution

The correct answer is Corrosion.

Key Points

  • Corrosion is when a refined metal is converted to a more stable form such as its oxide, hydroxide, or sulfide state this leads to deterioration of the material. It may be a result of some chemical process or it may occur naturally also. 
  • Rust is a form of corrosion, but it specifically refers to the oxidation of iron or its alloys. Only metals with iron or its alloys can get rusted.
  • Rust refers to the iron oxide that is produced in the process. For rusting to take place, there are certain necessary conditions. In the presence of oxygen and moisture or water, iron undergoes this reaction and form a series of iron oxide.
  • The reddish-brown color compound, known as rust is formed. If rusting starts at one place, it will eventually spread, and the whole metal will eventually disintegrate.

Chemical Reaction MCQAdditional Information

  • Corrosion in other metals:
    • Aluminum: Aluminum corrodes to form a thin layer of aluminum oxide forms over the surface of the metal, which acts as a protective barrier. This barrier doesn’t flake off like rust does, which prevents further corrosion of the aluminum in the future.
    • Copper: Copper corrodes to produces a green color compound known as patina. This patina is desirable as it not only forms a protective barrier to further corrosion but has a visual appeal that consumers like.

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