Chemical Reactions and Equations

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Case Based Questions for Ch 1 Chemical Reactions and Equations Class 10 Science

Important Questions

1

A chemical reaction is a representation of chemical change in terms of symbols and formulae of reactants and products. There are various types of chemical reactions like combination, decomposition, displacement, double displacement, oxidation and reduction reactions. Reactions in which heat is released along with the formation of products are called exothermic chemical reactions. All combustion reactions are exothermic reactions.

(i) The massive force that pushes the rocket forward through space is generated due to the

(a) combination reaction

(b) decomposition reaction

(c) displacement reaction

(d) double displacement reaction


(ii) A white salt on heating decomposes to give brown fumes and yellow residue is left behind. The yellow residue left is of

(a) lead nitrate

(b) nitrogen oxide

(c) lead oxide

(d) oxygen gas


(iii) Which of the following reactions represents a combination reaction?

(a) CaO (s) + H2O (l) ⟶ Ca(OH)2 (aq)

(b) CaCO3 (s) ⟶ CaO (s) + CO2(g)

(c) Zn(s) + CuSO4 (aq) ⟶ ZnSO4 (aq) + Cu(s)

(d) 2FeSO4(s) ⟶ Fe2O3 (s) + SO2(g) + SO3(g)


(iv) Complete the following statements by choosing correct type of reaction for X and Y.

Statement 1: The heating of lead nitrate is an example of ‘X’ reaction.

Statement 2: The burning of magnesium is an example of ‘Y’ reaction.

(a) X-Combination, Y-Decomposition

(b) X-Decomposition, Y-Combination

(c) X-Combination, Y-Displacement

(d) X- Displacement, Y-Decomposition

Answer

(i) (b) decomposition reaction
The massive force that pushes the rocket forward through space is generated due to the decomposition reaction. Hydrogen peroxide decomposes and provides it with a considerable reaction force thrust.

(ii) (c) lead oxide
Lead nitrate decomposes to give brown fumes of nitrogen dioxide gas and yellow residue of lead oxide is left behind.

(iii) (a) CaO (s) + H2O (l) ⟶ Ca(OH)2 (aq)
A reaction in which two or more reactants combine to form a single product is known as a combination reaction.

(iv) (b) X-Decomposition, Y-Combination

Lead nitrate decomposes to give lead oxide and nitrogen oxide. Thus, X is a decomposition reaction.

2Pb(NO3)2(s) ⟶ 2PbO(s) + 4NO2(g)

Magnesium burns in the presence of oxygen gas to magnesium oxide. Thus, Y is a combination reaction.

2Mg + O2 ⟶ 2MgO

2

Chemical reaction is a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products. Study this table related to the different types of reactions/processes.


(i) The reaction in which two or more substances combine to form a single substance under suitable conditions is:

(a) combination reaction

(b) combustion

(c) decomposition reaction

(d) photosynthesis


(ii) Which of the following is essential for photosynthesis?

(a) Sunlight

(b) Chlorophyll

(c) Glucose

(d) Both 'a' and 'b’


(iii) When a chemical compound decomposes on absorbing light and energy, then the reaction which takes place is known as:

(a) photosynthesis

(b) photodecomposition

(c) combination

(d) thermal decomposition


(iv) Which of the following reactions is an example of combustion reaction?

(a) C(s) + O2(g) ⟶ CO2(g)

(b) Zn(s) + H2SO4(aq) ⟶ ZnSO4 + H2(g)

(c) Zn(s) +2HCl(aq) ⟶ ZnCl2(aq) + H2(g)

(d) 3Mg(s) + N2(g) ⟶ Mg3N2(s)


(v) Which of the following is an example of combination reaction?

(a) H2 + Cl2 ⟶ 2HCl

(b) Fe + S ⟶ FeS

(c) 2H2 + O2 ⟶ 2H2O

(d) All of them

Answer

(i) (a) combination reaction

(ii) (d) Both 'a' and 'b’

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesis nutrients from carbon dioxide and water.


(iii) (b) photodecomposition

A photodecomposition is a chemical reaction in which an inorganic chemical (or an organic chemical) is broken down by photons and is the interaction of one or more photons with one target molecule.

(iv) (a) C(s) + O2(g) ⟶ CO2(g)

A combustion reaction is a reaction in which a substance reacts with oxygen gas, releasing energy in the form of light and heat.


(v) (d) All of them

A combination reaction (also known as a synthesis reaction) is a reaction where two or more elements or compounds (reactants) combine to form a single compound (product).

3

In the below experiment, when an iron nail is dipped in copper sulphate solution, a brown coating of copper is formed on the surface of the iron and the colour of the copper sulphate solution changes from blue to pale green. The reaction shows that iron is more reactive than copper because it displaces copper from the copper sulphate solution.


(i) The equation Cu + xHNO3 ⟶ Cu(NO3)2 + yNO2 + 2H2O

The values of x and y are:

(a) 3 and 5

(b) 8 and 6

(c) 4 and 2

(d) 7 and 1


(ii) What happens when copper rod is dipped in iron sulphate solution:

(a) Copper displaces iron

(b) Blue colour of copper sulphate solution is obtained

(c) No reaction takes place

(d) Reaction is exothermic


(iii) A substance which oxidised itself and reduces other is known as:

(a) Oxidising agent

(b) Reducing agent

(c) Both (a) and (b)

(d) None of these


(iv) Fe2O3 + 2Al ⟶ Al2O3 + 2Fe

The above reaction is an example of a:

(a) Combination reaction

(b) Double displacement reaction

(c) Decomposition reaction

(d) Displacement reaction


(v) Name the products formed when iron filings are heated with dilute hydrochloric acid.

(a) Fe (III) chloride and water

(b) Fe (II) chloride and water

(c) Fe (II) chloride and hydrogen gas

(d) Fe (III) chloride and hydrogen gas

Answer

(i) (c) 4 and 2

After balancing the equation, we get

Cu + 4HNO3 ⟶ Cu(NO3)2 + 2NO2 + 2H2O


(ii) (c) No reaction takes place.


(iii) (b) Reducing agent

Reducing agents reduce the other substance and in turn, get oxidized.


(iv) (d) Displacement reaction


(v) (c) Fe (II) chloride and hydrogen gas

When dilute Hydrochloric acid is added to iron filings, iron chloride & hydrogen gas is produced.

Fe + 2HCl ⟶ FeCl2 + H2

The iron displaces hydrogen from hydrochloric acid to form iron (II) chloride & hydrogen gas. This is a single displacement reaction.

4

Bleaching powder is also known as chloride of lime. It is solid and yellowish-white in colour. Bleaching powder can be easily identified by the strong smell of chlorine. When calcium hydroxide (slaked lime) reacts with chlorine, it gives calcium oxychloride (bleaching powder) and water is formed. Aqueous solution of bleaching powder is basic in nature. The material to be bleached is first passed through a solution of NaOH to remove greasy matter. Then it is passed through an aqueous solution of bleaching powder and very dil. HCl solution. HCl reacts with bleaching powder to liberate nascent oxygen which bleaches material.

(i) Bleaching powder is used as:

(a) bleaching agent in the textile, paper and jute industry

(b) disinfectant for water to make water free of germs

(c) oxidising agent in many industries

(d) all of these


(ii) Bleaching powder is also known as:

(a) calcium oxychloride

(b) calcium hypochlorite

(c) chloride of lime

(d) all of these


(iii) Bleaching powder gives smell of chlorine because it:

(a) is unstable

(b) gives chlorine on exposure to atmosphere

(c) is a mixture of chlorine and slaked lime

(d) contains excess of chlorine.


(iv) Select the correct statement(s) regarding bleaching powder.

(a) It is pale yellow powder having smell of chlorine.

(b) It is sparingly soluble in water and gives milky suspension when dissolved in water.

(c) As bleaching powder gives nascent oxygen, it shows bleaching property.

(d) All of these.


(v) Identify the product ‘X’ in the given reaction.

Ca(OH)2 + Cl2 ⟶ X + H2O

(a) CaOCl2

(b) CaCl2

(c) Ca(ClO3)2

(d) CaCO3

Answer

(i) (d) all of these

(ii) (d) all of these

(iii) (b) gives chlorine on exposure to atmosphere

Bleaching powder gives chlorine on exposure to air by reacting with CO2.

CaOCl2 + CO2 ⟶ CaCO3 + Cl2


(iv) (d) all of these.

(v) (a) CaOCl2

Ca(OH)2 + Cl2 ⟶ CaOCl2 + H2O

CaOCl2: calcium oxychloride (bleaching powder)

5

Oxidation has damaging effect on metals as well as on food. The damaging effect of oxidation on metal is studied as corrosion and that on food is studied as rancidity. The phenomenon due to which metals are slowly eaten away by the reaction of air, water and chemicals present in atmosphere, is called corrosion. For example, iron articles are shiny when new, but get coated with a reddish-brown powder when left for sometime. This process is known as rusting of iron. Rancidity is the process of slow oxidation of oil and fat (which are volatile in nature) present in the food materials resulting in the change of smell and taste in them.


(i) Rancidity can be prevented by:

(a) adding antioxidants

(b) packaging oily food in nitrogen gas

(c) both (a) and (b)

(d) none of these.


(ii) Combination of phosphorus and oxygen is an example of:

(a) oxidation

(b) reduction

(c) rancidity

(d) none of these


(iii) A science teacher wrote the following statements about rancidity:

(I) When fats and oils are reduced, they become rancid.

(II) In chips packet, rancidity is prevented by oxygen.

(III) Rancidity is prevented by adding antioxidants.

Select the correct option

(a) (I) only

(b) (II) and (III) only

(c) (III) only

(d) (I), (II) and (III)


(iv) Two statements are given below regarding rusting of iron.

(I) The rusting of iron is a redox reaction and reaction occurs as,

4Fe + 3O2 ⟶ 4Fe3+ + 6O2–

(II) The metallic iron is oxidised to Fe2+ and O2 is reduced to O2–.

Select the correct statement(s).

(a) I only

(b) II only

(c) Both I and II

(d) None of these


(v) Which of the following measures can be adopted to prevent or slow down rancidity?

(I) Food materials should be packed in air tight container.

(II) Food should be refrigerated.

(III)Food materials and cooked food should be kept away from direct sunlight.

(a) Only II and III

(b) Only I and III

(c) Only II and III

(d) I, II and III

Answer

(i) (c) both (a) and (b)

Antioxidants and nitrogen gas prevent oxidation of food.


(ii) (a) oxidation

4P + 3O2 ⟶ 2P2O3,

4P + 5O2 ⟶ 2P2O5


(iii) (III) only

The oils and fats are slowly oxidised to certain bad smelling compounds, which release foul smell. This is known as rancidity. Rancidity is prevented by filling nitrogen gas in chips packets.


(iv) (a) I only


(v) (d) I, II and III

6

Chemical equation is a method of representing a chemical reaction with the help of symbols and formulae of the substances involved in it. In a chemical equation, the substances which combine or react are called reactants and new substances produced are called products. A chemical equation is a short hand method of representing a chemical reaction. A balanced chemical equation has an equal number of atoms of different elements in the reactants and products side. An unbalanced chemical equation has unequal number of atoms of one or more elements in reactants and products. Formulae of elements and compounds are not changed to balance an equation.

(i) Consider the following reaction:

pMg3N2 + qH2O ⟶ rMg(OH)2 + sNH3

When the equation is balanced, the coefficients p, q, r, s respectively are:

(a) 1, 3, 3, 2

(b) 1, 6, 3, 2

(c) 1, 2, 3, 2

(d) 2, 3, 6, 2


(ii) Which of the following information is not conveyed by a balanced chemical equation?

(a) Physical states of reactants and products

(b) Symbols and formulae of all the substances involved in a particular reaction

(c) Number of atoms/molecules of the reactants and products formed

(d) Whether a particular reaction is actually feasible or not


(iii) The balancing of chemical equations is in accordance with

(a) law of combining volumes

(b) law of constant proportions

(c) law of conservation of mass

(d) both (b) and (c)


(iv) Which of the following chemical equations is an unbalanced one?

(a) 2NaHCO3 ⟶ Na2CO3 + H2O + CO2

(b) 2C4H10 + 12O2 ⟶ 8CO2 + 10H2O

(c) 2Al + 6H2O ⟶ 2Al(OH)3 + 3H2

(d) 4NH3 + 5O2 ⟶ 4NO + 6H2O


(v) Which of the following statements is/are correct?

(a) A chemical equation tells us about the substances involved in a reaction.

(b) A chemical equation informs us about the symbols and formulae of the substances involved in a reaction.

(c) A chemical equation tells us about the atoms or molecules of the reactants and products involved in a reaction.

(d) All the above.

Answer

(i) (b) 1, 6, 3, 2

After balancing the equation, we get

Mg3N2 + 6H2O ⟶ 3Mg(OH)2 + 2NH3

 

(ii) (d) Whether a particular reaction is actually feasible or not

 

(iii) (c) law of conservation of mass

In a balanced chemical equation, total mass of reactants must be equal to the total mass of products. This is the statement of law of conservation of mass.

 

(iv) (b) 2C4H10 + 12O2 ⟶ 8CO2 + 10H2O

 

(v) (d) All the above.

7

Redox reactions are those reactions in which oxidation and reduction occur simultaneously. A redox reaction is made up of two half reactions. In the first half reaction, oxidation takes place and in second half reaction, reduction occurs. Oxidation is a process in which a substance loses electrons and in reduction, a substance gains electron. The substance which gains electrons is reduced and acts as an oxidising agent. On the other hand, a substance which loses electrons is oxidised and acts as a reducing agent.

(i) Which of the following is a redox reaction?

(a) CaCO3 ⟶ CaO + CO2

(b) H2 + Cl2 ⟶ 2HCl

(c) CaO + 2HCl ⟶ CaCl2 + H2O

(d) NaOH + HCl ⟶ NaCl + H2O


(ii) Identify the reaction in which H2O2 is acting as a reducing agent.

(a) H2SO3 + H2O2 ⟶ H2SO4 + H2O

(b) 2HI + H2O2 ⟶ 2H2O + I2

(c) Cl2 + H2O2 ⟶ 2HCl + O2

(d) 2FeCl2 + 2HCl + H2O2 ⟶ 2FeCl3 + 2H2O


(iii) For the following reactions, identify the one in which H2S acts as a reducing agent.

(a) CuSO4 + H2S ⟶ CuS + H2SO4

(b) Cd(NO3)2 + H2S ⟶ CdS + 2HNO3

(c) 2FeCl3 + H2S ⟶ 2FeCl2 + 2HCl + S

(d) None of these


(iv) For the following reaction, identify the correct statement.

ZnO + CO ⟶ Zn + CO2

(a) ZnO is being reduced.

(b) CO2 is being oxidised.

(c) CO is being reduced.

(d) ZnO is being oxidised.


(v) In the following reaction, which substance is reduced?

Pbs + 4H2O2 ⟶ PbSO4 + 4H2O

(a) H2O

(b) H2O2

(c) PbS

(d) PbSO4

Answer

(i) (b) H2 + Cl2 ⟶ 2HCl

H2 is oxidised to HCl while Cl2 is reduced to HCl.

 

(ii) (c) Cl2 + H2O2 ⟶ 2HCl + O2

 

(iii) (c) 2FeCl3 + H2S ⟶ 2FeCl2 + 2HCl + S

H2S itself gets oxidised to S and reduces FeCl3 to FeCl2.

 

(iv) (a) ZnO is being reduced. ZnO is reduced to Zn and CO is oxidised to CO2.

 

(v) (b) H2O2 is reduced to water by removal of oxygen.

8

In a chemical reaction, reactants are converted into products. The conversion of reactants into products in a chemical reaction is often accompanied by some features which can be observed easily. These easily observed features which take place as a result of chemical reaction are known as characteristics of chemicals reactions. Some important characteristics of chemical reactions are:

(I) Evolution of heat

(II) Formation of precipitate

(III) Change in colour

(IV) Change in temperature

(V) Change in state

Any one of these general characteristics can tell us whether a chemical reaction has taken place or not.


(i) Reaction of magnesium with air is a/an:

(a) exothermic reaction

(b) endothermic reaction

(c) reversible reaction

(d) substitution reaction


(ii) In the following reaction,

Ca2+(aq) + 2OH-(aq) ⟶ Ca(OH)2(s)

precipitate of calcium hydroxide will be of:

(a) green colour

(b) blue colour

(c) brown colour

(d) white colour.


(iii) In the given reaction,

S(s) + O2(g) ⟶ SO2

the physical state of SO2 is

(a) liquid

(b) solid

(c) gaseous

(d) all three.


(iv) Which one of the following processes involve chemical reactions?

(a) Storing of oxygen gas under pressure in a gas cylinder.

(b) Keeping petrol in a china dish in the open.

(c) Liquefaction of air.

(d) Heating copper wire in the presence of air at high temperature.


(v) In which of the following reactions, high amount of heat energy will be evolved?

(a) Electrolysis of water

(b) Dissolution of NH4Cl in water

(c) Burning of L.P.G.

(d) Decomposition of AgBr in the presence of light.

Answer

(i) (a) exothermic reaction

 

(ii) (d) white colour.

Calcium hydroxide is a white colour solid.

 

(iii) (c) gaseous

SO2 is gaseous in nature.

 

(iv) (d) Heating copper wire in the presence of air at high temperature.

When copper is heated in the presence of air in a very high temperature, a chemical reaction takes place. Copper reacts with oxygen of the air to form a thin layer of copper oxide on the surface of metallic copper.

 

(v) (c) Burning of L.P.G.

On burning of L.P.G., heat is evolved.

9

Reactions in which one element takes place of another element in a compound, are known as displacement reactions. In general, more reactive elements displaces a less reactive element from its compound. In all single displacement reactions, only one element displaces another element from its compound. The single displacement reactions are, however, written as just displacement reactions. The displacement reaction between iron (III) oxide and powdered aluminium produces so much heat that iron metal obtained is in molten form.

(i) Copper displaces which of the following metals from its salt solution?

(a) ZnSO4

(b) FeSO4

(c) AgNO3

(d) NiSO4


(ii) When zinc reacts with dilute sulphuric acid, the gas evolved is

(a) red in colour and have a sweet smelling.

(b) green in colour and have a foul smell.

(c) colourless, odourless and burns with a pop sound.

(d) colourless, pungent smelling and burns with a pop sound.


(iii) When dry hydrogen is passed over a heated oxide of metal X using the apparatus shown below, a reddish-brown residue is obtained.


The reddish-brown residue could be

(a) copper

(b) lead

(c) silver

(d) zinc


(iv) Which of the following reactions is a displacement reaction?

(a) CaO + H2O ⟶ Ca(OH)2

(c) Mg + CuSO4 ⟶ MgSO4 + Cu

(b) MgCO3 ⟶ Mg + CO2

(d) H2 + Cl2 ⟶ 2HCl


(v) When dilute hydrochloric acid is added to granulated zinc placed in a test tube, the observation made is

(a) the surface of the metal turns shining

(b) the reaction mixture turns milky

(c) greenish yellow gas is evolved

(d) the colourless and odourless gas evolves burns with a pop sound.

Answer

(i) (c) AgNO3

Cu + 2AgNO3 ⟶ Cu(NO3)2 + 2Ag

Copper can displace silver from its salt solution since, copper is more reactive than silver.

 

(ii) (c) colourless, odourless and burns with a pop sound.

Zn + H2SO4(dil.) ⟶ ZnSO4 + H2↑

H2 is a colourless, odourless gas and burns with a pop sound.

 

(iii) (a) Copper is the reddish-brown residue as shown in below reaction.


 

(iv) (c) Mg + CuSO4 ⟶ MgSO4 + Cu

It is a single displacement reaction.

 

(v) (d) the colourless and odourless gas evolves burns with a pop sound.

Hydrogen gas is evolved in this reaction as shown in the reaction.

Zn + 2HCl ⟶ ZnCl2 + H2↑

Hydrogen gas is colourless and odourless which burns with a pop sound.

10

Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions. A double displacement reaction usually occurs in solution and one of the products, being insoluble, precipitate out (separates as a solid). Any reaction in which an insoluble solid (called precipitate) is formed that separates from the solution is called a precipitation reaction. The reaction in which acid or acidic oxide reacts with base or basic oxide to form salt and water is called neutralisation reaction.

For example, 2NaOH + H2SO4 ⟶ Na2SO4 + H2O


(i) When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of a:

(a) combination reaction

(b) displacement reaction

(c) decomposition reaction

(d) double displacement reaction


(ii) Which of the following is not a double displacement reaction?

(a) AgNO3(aq) + NaCl(aq) ⟶ AgCl(s) + NaNO3(aq)

(b) Zn(s) + H2SO4(aq) ⟶ ZnSO4(aq) + H2(g)

(c) CuSO4(aq) + H2S (aq) ⟶ CuS(s) + H2SO4(aq)

(d) Pb(NO3)2(aq) + 2KI (aq) ⟶ PbI2(s) + 2KNO3(aq)


(iii) Barium chloride on reaction with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?

(I) Displacement reaction

(II) Precipitation reaction

(III) Combination reaction

(IV) Double displacement reaction

(a) (I) only

(b) (II) only

(c) (III) and (IV) only

(d) (II) and (IV) only


(iv) Identify A in the following reaction.

AlCl3(aq) + 3NH4OH(aq) ⟶ A + 3NH4Cl(aq)

(a) Al(OH)3

(b) Al2O3

(c) AlH3

(d) AlN


(v) Consider the following reaction,

BaCl2 + Na2SO4 ⟶ BaSO4 + 2NaCl

Identify the precipitate in the reaction.

(a) BaCl2

(b) BaSO4

(c) Na2SO4

(d) NaCl

Answer

(i) (d) double displacement reaction

CuSO4 + H2S ⟶ CuS + H2SO4

Both CuSO4 and H2S exchange their ions to give new compounds- CuS and H2SO4. Hence, this is a double displacement reaction.

 

(ii) (b) Zn(s) + H2SO4(aq) ⟶ ZnSO4(aq) + H2(g)

It is an example of single displacement reaction.

 

(iii) (d) (II) and (IV) only

BaCl2 + (NH4)2SO4 ⟶ BaSO4↓ + 2NH4Cl

(BaSO4: white ppt.)

It is a precipitation reaction as well as double displacement reaction.

 

(iv) (a) Al(OH)3

AlCl3 + 3NH4OH ⟶ Al(OH)3 + 3NH4Cl

 

(v) (b) BaSO4

BaCl2(aq) + Na2SO4(aq) ⟶ BaSO4(s) ↓ + 2NaCl(aq)

(BaSO4: white ppt.)

11

The earlier concept of oxidation and reduction is based on the addition or removal of oxygen or hydrogen elements so, in terms of oxygen and hydrogen, oxidation is addition of oxygen to a substance and removal of hydrogen from a substance. On the other hand, reduction is addition of hydrogen to a substance and removal of oxygen from a substance. The substance which gives oxygen to another substance or removes hydrogen from another substance in an oxidation reaction is known as oxidising agent, while the substance which gives hydrogen to another substance or removes oxygen from another substance in a reduction reaction is known as reducing agent. For example,


(i) A redox reaction is one in which:

(a) both the substances are reduced

(b) both the substances are oxidized

(c) an acid is neutralised by the base

(d) one substance is oxidised while the other is reduced.


(ii) In the reaction, H2S + Cl2 ⟶ S + 2HCI

(a) H2S is the reducing agent.

(c) H2S is the oxidising agent.

(b) HCl is the oxidising agent.

(d) Cl2 is the reducing agent.


(iii) Which of the following processes does not involve either oxidation or reduction?

(a) Formation of slaked lime from quick lime.

(b) Heating mercuric oxide.

(c) Formation of manganese chloride from manganese oxide (MnO2).

(d) Formation of zinc from zinc blend.


(iv) Mg + CuO ⟶ MgO + Cu

Which of the following is wrong relating to the above reaction?

(a) CuO gets reduced.

(b) Mg gets oxidised.

(c) CuO gets oxidised.

(d) It is a redox reaction.


(v) Identify the correct oxidising agent and reducing agent in the following reaction.

Fe2O3 + 2AI ⟶ 2Fe + Al2O3

(a) Al - Oxidising agent, Fe2O3 - Reducing agent

(b) Fe2O3 - Oxidising agent, Al - Reducing agent

(c) Fe - Oxidising agent, Al2O3 - Reducing agent

(b) Fe2O3 - Oxidising agent, Al2O3 - Reducing agent

Answer

(i) (d) one substance is oxidised while the other is reduced.

In a redox reaction, one reactant is reduced while other reactant is oxidised.

 

(ii) (a) H2S is the reducing agent.

 

(iii) (a) Formation of slaked lime from quick lime

It is a decomposition reaction.

 

(iv) (c) CuO gets oxidised.

Addition of oxygen is called oxidation while the removal of oxygen is called reduction.

Thus, Mg gets oxidised and CuO gets reduced and it is a redox reaction.

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