Category: Class 12 Chemistry Objective Questions

Chemistry Multiple Choice Questions on “Alcohols and Phenols – 1”.

1. How are alcohols prepared from haloalkanes?
a) By treating with concentrated H₂SO₄
b) By heating with aqueous NaOH
c) By treating with a strong reducing agent
d) By treating with Mg metal
Answer: b
Clarification: Haloalkanes when heated with aqueous NaOH or KOH give respective alcohols. This is a nucleophilic substitution reaction where the halide group is replaced by the OH nucleophile.

2. Which of the following process do not yield alcohols?
a) Acid catalysed hydration of alkenes
b) Hydroboration-oxidation of alkenes
c) Reduction of aldehydes
d) Free radical halogenation of alkanes
Answer: d
Clarification: Alkanes on free radical halogenation produce a mixture of haloalkanes and not alcohols. Alcohols can be prepared from alkenes by acid catalysed hydration and hydroboration-oxidation or from reduction of aldehydes.

3. Identify the catalyst in the hydration of alkenes to produce alcohols.
a) HCl
b) FeCl₃
c) Pt
d) Ni
Answer: a
Clarification: Alkenes react with water in the presence of a mineral acid as a catalyst to form alcohols. The H+ ion from the acid helps to form a carbocation for nucleophilic attack.

4. Propene when reacted with water in the presence of H₂SO₄ gives _________
a) Propan-1-ol
b) Propan-2-ol
c) 2-Methylpropan-1-ol
d) 2-Methylpropan-2-ol
Answer: b
Clarification: Since propene is an unsymmetrical alkene, the given hydration reaction takes place in accordance to Markovnikov’s rule, to form propan-2-ol. The double bond is broken and the OH group attaches at the second carbon.

5. The first step of the acid catalysed hydration of alkenes, involves the protonation of alkene to form a carbocation by electrophilic attack of _______
a) H⁺
b) H₂O
c) H₃O⁺
d) OH^–
Answer: c
Clarification: The water reacts with the H⁺ ion of the mineral acid to form a hydronium ion (H₃O⁺). This ion attacks the carbon double bond to form a carbocation and give a water molecule.

6. Identify the nucleophile that attacks the carbocation in the second step of acid catalysed hydration of alkenes?
a) OH^–
b) H₂O
c) H⁺
d) H₃O⁺
Answer: b
Clarification: Nucleophiles are electron rich species that attack the part of the structure that is electron deficient. In this step, the H₂O nucleophile attacks the carbocation forming a protonated alcohol.

7. Name the following step from the mechanism of acid catalysed hydration of ethene.

a) Protonation
b) Electrophilic attack
c) Nucleophilic attack
d) Deprotonation
Answer: d
Clarification: In this step, the electron pair of water attack the protonated alcohol, resulting in the loss of H⁺ from oxygen (deprotonation) to form an alcohol.

8. Which compound reacts with propene to form tripropyl borane?
a) Borane
b) Diborane
c) Boric acid
d) Sodium borohydride
Answer: b
Clarification: Diborane (B₂H₆) reacts with alkenes to give trialkyl boranes as a product of successive addition. Firstly, CH₃CH₂CH₂(BH₂) is formed which reacts with propene to give (CH₃CH₂CH₂)₂BH, which further reacts with propene to finally give (CH₃CH₂CH₂)B, which is tripropyl borane.

9. Which of the following is not required for the conversion of trialkyl borane to an alcohol?
a) Diborane
b) Water
c) Sodium hydroxide
d) Hydrogen peroxide
Answer: a
Clarification: Trialkyl boranes are oxidised by hydrogen peroxide in the presence of aqueous NaOH to form alcohols. Diborane is not required for this conversion but is essential in the production of trialkyl boranes.

10. Propan-2-ol can be prepared form the hydroboration-oxidation of propene.
a) True
b) False
Answer: b
Clarification: The oxidation of trialkyl boranes proceeds according to anti-Markovnikov’s rule, and hence the product formed will be propan-1-ol.

11. What happens when an aldehyde is treated with lithium aluminium hydride?
a) Primary alcohol is formed
b) Secondary alcohol is formed
c) Tertiary alcohol is formed
d) No reaction
Answer: a
Clarification: LiAlH₄ acts as a reducing agent which reduces an aldehyde by adding hydrogen atoms to it result in the formation of a primary alcohol.

12. Which carbonyl compound yields secondary alcohols when treated with LiAlH₄?
a) Aldehyde
b) Ketone
c) Carboxylic acid
d) Ester
Answer: b
Clarification: Ketones react with reducing agents LiAlH₄ or NaBH₄ to get reduced to alcohol where the OH group is formed at the C of the C-O group. This results in the C being bonded to two alkyl groups apart from the OH and H atom.

13. Esters on catalytic hydrogenation always give a mixture of two different alcohols.
a) True
b) False
Answer: b
Clarification: Esters (RCOOR’) give a mixture of two alcohols depending upon the acyl group (RCO^–) and the alkoxy group (-OR’). Methyl acetate (CH₃COOCH₃) gives a mixture of methanol and ethanol, whereas ethyl acetate (CH₃COOCH₂CH₃) gives only ethanol.

14. Hydrolysis of the adduct formed form the reaction of ________ with methyl magnesium bromide gives 2-Methylpropan-2-ol.
a) Methanal
b) Ethanal
c) Propanal
d) Propanone
Answer: d
Clarification: 2-Methylpropan-2-ol is a tertiary alcohol which is produced from the hydrolysis of the adduct formed between a ketone and a Grignard reagent.

15. Which of the following aldehydes can produce 1o alcohols when treated with Grignard reagent?
a) Methanal
b) Ethanal
c) Propanal
d) Butanal
Answer: a
Clarification: Methanal on treatment with Grignard reagent forms an adduct which has only one alkyl group attached to the C atom along with two hydrogens and one O-Mg-X (X=halogen) group. This on hydrolysis will form a primary alcohol where the OH group will replace the O-Mg-X group.

Chemistry Multiple Choice Questions on “Carboxylic Acids Chemical Reactions – 1”.

1. The reaction of carboxylic acids with NaHCO₃ produces ______ which helps it to differentiate it from phenols.
a) H₂O
b) CO
c) CO₂
d) NaCl
Answer: c
Clarification: Unlike phenols, carboxylic acids react with weak bases like hydrogen carbonates to give carbon dioxide, along with sodium carboxylate salt and water.

2. The pK_a value is equivalent to ________
a) logK_a
b) -logK_a
c) logK_eq
d) -logK_eq
Answer: b
Clarification: K_eq is the equilibrium constant of a reaction and K_a is the acid dissociation constant which is K_eq[H₂O]. The strength of an acid is generally by its pK_a value rather than its K_a value.

3. If the pK_a value of acetic acid is 4.76, predict the pK_a value of HCl.
a) -7
b) 4.2
c) 7
d) 10
Answer: a
Clarification: Generally, carboxylic acids are weaker acids than mineral acids like hydrochloric acid. Also, mineral acids are strong with pK_a values usually less than 1. Hence, the pK_a value of carboxylic acids will be higher.

4. What is the relation between the acidic strength of A and B?

a) A = B
b) A > B
c) A d) A >> B

Answer: c
Clarification: Compound A has a methoxy group (electron donating) and compound B has nitro group (electron withdrawing). In simple terms, the electron withdrawing groups stabilise the carboxylate ion and strengthen the acid, whereas electron donation groups weaken the acid.

5. Which of the following is the stronger acid?
a) Acetic acid
b) Propanoic acid
c) Isobutyric acid
d) 2,2-Dimethylpropanoic acid
Answer: a
Clarification: As the size of alkyl group (electron releasing) increases, the electron density on the O of OH group increases, and makes release of H⁺ ion more difficult. Thus, the release of proton from acetic acid will be easier compared to the higher acids, and is therefore the stronger acid.

6. Which of the following is the strongest acid?
a) CH₃COOH
b) CH₂ClCOOH
c) CHCl₂COOH
d) CCl₃COOH
Answer: d
Clarification: The -I inductive effect increases as the number of Cl atoms (electron withdrawing substituents) increases. The carboxylate ion becomes more stable as more negative charge is dispersed, thereby strengthening the acid.

7. Which of the following has the highest pK_a value?
a) Bromoacetic acid
b) Chloroacetic acid
c) Fluoroacetic acid
d) Iodoacetic acid
Answer: d
Clarification: Higher the electronegativity of a halogen, greater will be its electron withdrawing effect, and stronger will be the acid. Since electronegativity of halogens decrease in the order F > Cl > Br > I, iodoacetic acid will be the weakest and hence will have the highest pK_a value.

8. Which of the following will have the highest acidic strength?
a) Butanoic acid
b) 2-Chlorobutanoic acid
c) 3-Chlorobutanoic acid
d) 4-Chlorobutanoic acid
Answer: b
Clarification: Halogen substituted carboxylic acids are stronger acid than their respective parent acids, because of the electron withdrawing and stabilizing nature of the halogen. Furthermore, as the distance of the halogen form the COOH group increases, the electron withdrawing influence decreases, and therefore the acidic character decreases.

9. What is the correct order of acidity of the following?
a) Acetic acid > Acrylic acid > Propiolic acid
b) Acetic acid > Propiolic acid > Acrylic acid
c) Propiolic acid > Acrylic acid > Acetic acid
d) Acrylic acid > Propiolic acid > Acetic acid
Answer: c
Clarification: The electronegativity of carbon increases from sp³ to sp² to sp hybridisation. The carbon attached to the carbonyl carbon of propionic acid id sp hybridised (due to triple bond) ang has a higher inductive effect on the COOH group and as a result has higher acidity compared to acrylic acid (sp² carbon) or acetic acid (sp³ carbon).

10. It is given that the following compound has a higher pK_a value than benzoic acid. Which is the most probable substituent group X of the compound?

a) OH
b) Cl
c) CN
d) NO₂
Answer: a
Clarification: Given that the compound has a higher pK_a value than benzoic acid, it should have weaker acidic strength than benzoic acid. This means, that X should be an electron donating group that destabilises the compound and reduces its acidic strength. Since is an electron releasing group, the X group should be OH.

11. Acrylic acid is a stronger acid than benzoic acid.
a) True
b) False
Answer: b
Clarification: Both compounds contain a sp² hybridised carbon atom next to the COOH group, but the double bond of a benzene ring is less electron releasing in nature than the vinyl carbon double bond of acrylic acid. This is because delocalisation in the resonance structures of benzoic acid destroys its aromatic character. Hence, benzoic acid is stronger than acrylic acid.

12. What is the correct order of pK_a values of the following acids?
a) Benzoic acid > m-Nitrobenzoic acid > p-Nitrobenzoic acid
b) Benzoic acid > p-Nitrobenzoic acid > m-Nitrobenzoic acid
c) p-Nitrobenzoic acid > m-Nitrobenzoic acid > Benzoic acid
d) m-Nitrobenzoic acid > p-Nitrobenzoic acid > Benzoic acid
Answer: a
Clarification: Nitro group is electron withdrawing in nature and increases the acidic strength of acids. The electron withdrawing effect of NO₂ is pronounced at para position more than meta position, hence the p-isomer is more acidic and has a lower pK_a value than m-isomer.

13. Which of the following is the most acidic?
a) Benzoic acid
b) o-Toluic acid
c) m-Toluic acid
d) p-Toluic acid
Answer: b
Clarification: Although CH₃ is an electron releasing group and should reduce the acidic character of acids by destabilizing it, the presence of CH₃ group at ortho position has a reverse effect and increases the acidic strength compared to benzoic acid. This is due to a combination of stearic and electronic factors.

14. Which of the following has a higher acidic character than benzoic acid?
a) Acetic acid
b) p-Methoxybenzoic acid
c) p-Bromobenzoic acid
d) p-Aminobenzoic acid
Answer: c
Clarification: Bromine is an electron withdrawing group that disperse the negative charge on the carboxylate ion and strengthens its acidic character. p-Bromobenzoic acid has a pK_a value of 3.96 compared to 4.19, which is the pK_a value of benzoic acid.

15. The presence of CF₃ group in an acid gives a higher acidic strength compared to the presence of NO₂.
a) True
b) False
Answer: a
Clarification: CF₃ group is highly electronegative due to the presence of three F atoms and has a greater electron withdrawing and stabilizing influence on carboxylate ion than NO₂ group.

Chemistry Multiple Choice Questions on “Diazonium Salts Physical Properties”.

1. Aromatic diazonium salts are stable at _____ temperatures.
a) cold
b) room
c) warm
d) high
Answer: a
Clarification: Benzenediazonium salts are stable in cold environment, but readily react with water when the temperature increases even slightly.

2. When a blue litmus paper is dipped in an aqueous solution of benzenediazonium bromide, the litmus paper _____
a) turns red
b) turns orange
c) turns black
d) remains unchanged
Answer: d
Clarification: Benzenediazonium bromide is a salt, made of a positive diazonium group and a negative bromide ion. Thus, it remains neutral to litmus paper.

3. Benzenediazonium chloride is ______ in water.
a) slightly soluble
b) highly soluble
c) insoluble
d) highly insoluble
Answer: b
Clarification: Benzenediazonium chloride is readily soluble in polar solvents like water. However, it is less soluble in solvents like alcohol.

4. Which of the following best describes benzenediazonium chloride?
a) Yellow solid
b) Colourless crystals
c) White powder
d) Oily liquid
Answer: b
Clarification: Benzenediazonium chloride is usually obtained in crystal form. It is unstable and formed for a short period when aniline reacts with nitrous acid. It is a salt with chlorine as the negative group and diazo group as positive.

5. Which of the following diazonium salts is insoluble in water?
a) C₆H₅N₂⁺Cl^–
b) C₆H₅N₂⁺Br^–
c) C₆H₅N₂⁺HSO₄^–
d) C₆H₅N₂⁺BF₄^–
Answer: d
Clarification: Certain diazonium salts such as fluoroborates are insoluble in water. This makes them stable enough to be dried and stored.

6. Which of the following properties is suitable for all diazonium salts?
a) Water soluble
b) Coloured solids
c) Explosive
d) Unreactive
Answer: c
Clarification: Diazonium salts are unstable and may explode in dry state. Therefore, they are generally used in solution or aqueous state.

7. Benzenediazonium chloride is commercially available in packaged form.
a) True
b) False
Answer: b
Clarification: Because of the highly unstable nature of diazonium salts, they are not commercially available. Instead, they are prepared on demand.

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Chemistry Multiple Choice Questions on “Types of Polymerisation Reactions – 1”.

1. Addition polymerisation is also known as _________
a) copolymerisation
b) homopolymerisation
c) step growth polymerisation
d) chain growth polymerisation
View Answer

Answer: d
Clarification: Addition polymerisation takes place through steps leading to the increase in chain length and each step produces reactive intermediates for use in the next stage of the growth of the chain. It may take place between molecules of the same monomer or different monomers.

2. Which of the following cannot undergo addition polymerisation?
a) Ethane
b) Ethene
c) Propylene
d) Vinyl benzene
Answer: a
Clarification: The monomers involved in addition polymerisation are unsaturated compounds like alkenes and alkadienes. This is because it does not involve the removal of any molecule and hence requires the breaking of a double bond for it to progress.

3. Which of the following is not a type of addition polymerisation?
a) Free radical polymerisation
b) Polycondensation polymerisation
c) Anionic polymerisation
d) Cationic polymerisation
Answer: b
Clarification: Depending on the nature of the reactive species involved, addition polymerisation is classified as free radical, anionic and cationic based on whether the initiator is a free radical, anion or cation respectively.

4. Which of the following is not a suitable initiator for free radical addition polymerisation reaction?
a) Acetyl peroxide
b) Benzoyl peroxide
c) tert-Butyl peroxide
d) Benzoquinone
Answer: d
Clarification: Benzoquinone combines with the free radical intermediate to form a highly stable, non-reactive radical because of resonance. This inhibits the further progress of the chain growth and therefore, the reaction stops. Peroxides are very important free radical generating initiators.

5. In free radical mechanism, the step in which two very large free radicals combine with each other is called the _______ step.
a) chain initiating
b) chain propagating
c) chain growth
d) chain terminating
Answer: d
Clarification: The final step in which the product radical react with each other to form a polymerised product is called the chain terminating step. The other two steps involve reaction of one free radical with the unsaturated molecule.

6. Identify the chain initiation step of the polymerisation of ethene in the presence of benzoyl peroxide initiator, from the following?
a) C₆H₅• + C₂H₄ = C₆H₅-CH₂-CH₂•
b) C₆H₅-CH₂-CH₂• + C₂H₄ = C₆H₅-CH₂-CH₂-CH₂-CH₂•
c) C₆H₅-CH₂-CH₂-CH₂-CH₂• = C₆H₅-(-CH₂-CH₂-)_n-CH₂•
d) C₆H₅-(-CH₂-CH₂-)_n-CH₂• + C₆H₅-(-CH₂-CH₂-)_n-CH₂• = C₆H₅-(-CH₂-CH₂-)_n-C₆H₅
Answer: a
Clarification: Benzoyl peroxide undergoes homolytic fission to from phenyl free radical which acts an initiator. The first step is the addition of this radical to the ethene double bond, thus generating a new and larger free radical. This is called the chain initiating step.

7. Which of the following statements is correct regarding LDP and HDP?
a) Both have different monomers
b) Both have same structures
c) Both have similar preparation conditions
d) Both are chemically inert
Answer: d
Clarification: Low-density and high-density polythene have the same monomeric unit, ethene. Both are synthesized under very different pressure and temperatures conditions. LDP has a branches whereas HDP is a linear structure. Both are chemically inert and tough.

8. Identify the most suitable catalyst for the reaction shown.

a) Dioxygen
b) Ziegler-Natta catalyst
c) Persulphate
d) AlCl₃
Answer: c
Clarification: This is the addition polymerisation of tetrafluoroethene to give Teflon. It is carried out in the presence of a free radical or persulphate catalyst at high pressures.

9. LDP is used in the making of electrical wires.
a) True
b) False
Answer: a
Clarification: LDP is chemically inert and tough but flexible and a poor conductor of electricity. This makes it suitable for use in the insulation of electricity carrying wires.

10. Which of the following is not suitable for the polymerisation of ethene to form high-density polythene?
a) Presence of Ziegler-Natta catalyst
b) Temperature of 500K
c) Pressure of 7 atmospheres
d) Hydrocarbon solvent
Answer: b
Clarification: HDP is formed when polymerisation of C₂H₄ takes place through addition in a hydrocarbon solvent with Ziegler-Natta catalyst at temperature of 333-343K and under a pressure of 6-7 atmospheres. Temperatures and pressure higher than this will favour the formation of LDP.

11. Polymerisation of vinyl cyanide with peroxide catalyst forms _______
a) PVC
b) PAN
c) PET
d) HDP
Answer: b
Clarification: Polyacrylonitrile (PAN) is a polymerised product of acrylonitrile (vinyl cyanide) in the presence of a peroxide catalyst. Vinyl cyanide can be prepared by treating ethyne with HCN in the presence of Ba(CN)₂ catalyst. PAN is used for making orlon and acrilan.

12. Which of the following is used in non-stick pans?
a) HDP
b) LDP
c) Teflon
d) Orlon
Answer: c
Clarification: Teflon (polymer of tetrafluoroethene) is chemically inert and resistant to attacks by corrosive agents. This makes it suitable for use in making oil seals, gaskets and also in non-stick surface coated utensils.

13. What are the monomers of dacron?
a) Ethane-1,2-diol and terephthalic acid
b) Ethylene glycol and phthalic acid
c) 1,3-Butadiene and terephthalic acid
d) Ethylene glycol and 1,3-butadiene
Answer: a
Clarification: Dacron or terylene is a condensation polymer formed by the step growth polymerisation of ethylene glycol and terephthalic acid.

14. Terylene is a polyamide.
a) True
b) False
Answer: b
Clarification: Terylene is a polycondensation product of a dicarboxylic acid (terephthalic acid) and a diol (ethylene glycol) involving ester (COO) linkages. Hence, it is a polyester.

Chemistry Multiple Choice Questions on “Imperfections in Solids”.

1. What kind of order is present in a solid for it to be a perfectly crystalline solid?
a) Long range order
b) Short range order
c) No order
d) Both, short range and long range order
Answer: d
Clarification: Only short range order is a feature of amorphous solids. Crystalline solids exhibit both short and long range order. Crystalline solids are formed by repetitive arrangement of unit cells.

2. State whether true or false: The number of defects in a crystal can be minimized by carrying out the process of crystallization at a slow rate.
a) True
b) False
Answer: a
Clarification: All big crystals have some or the other defects in the arrangement of their constituents. An ideal crystal does not exist. These defects are more if the crystallization process occurs at a faster rate. Hence, slowing down the process minimizes the defects. It is akin to starting with one crystal (unit) and adding to it from all sides to create a bigger crystal. Defects are produced due to some irregularity in this arrangement.

3. In a crystal, if a fault exists in the arrangement at a point, it is called as _________
a) space defect
b) single defect
c) point defect
d) primary defect
Answer: c
Clarification: When there is a fault in the arrangement of a constituent particle such as an atom, ion or molecule, and the fault exists at a point in the lattice structure, it is called as a point defect.

4. In which type of point defect are the cations and anions absent in stoichiometric proportions?
a) Schottky defect
b) Frenkel defect
c) Impurity defect
d) The given situation does not occur for any point defect.
Answer: a
Clarification: A vacancy defect is when an atom, ion or molecule is absent from its position in the lattice. When this occurs for ionic solids, it is called a Schottky defect. Cations and anions are found to be absent in stoichiometric proportion so that the electrical neutrality of the crystal is maintained.

5. Schottky defects are observed in solids with cations and anions of similar sizes. Which of the following compounds, therefore, is NOT likely to have a Schottky defect?
a) NaCl
b) AgCl
c) CsCl
d) KCl
Answer: b
Clarification: There is a considerable size difference between Ag cation and Cl anion. Hence a Frenkel defect is more likely to occur than a Schottky defect.

6. Impurity defect is a type of point defect. It can occur __________
a) in one way, as substitution impurity defect
b) in one way, as interstitial impurity defect
c) in two ways, as substitution impurity defect or as interstitial impurity defect
d) in two ways, as vacant impurity defect or as interstitial impurity defect
Answer: c
Clarification: An impurity defect occurs when a regular ion is replaced by some other type of ion, e.g. Na⁺ is replaced by K⁺. If the replacement occurs in the place of the regular cation, it is called a substitution impurity defect. If the replacement occurs in an interstitial position, it is called an interstitial impurity defect.

7. Stainless steel is a/an ________ alloy.
a) vacant
b) interstitial
c) substitution
d) pure
Answer: b
Clarification: Stainless steel is an interstitial alloy. Carbon atoms are introduced into interstitial spaces of iron lattice as an impurity. Further alloying sees the introduction of nickel, chromium in the interstitial spaces.

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Chemistry Multiple Choice Questions on “Electrochemistry – Batteries”.

1. A battery is an arrangement of electrolytic cells.
a) True
b) False
Answer: b
Clarification: A battery is not an arrangement of electrolytic cells, but an arrangement of electrochemical cells. An electrochemical cell is one which converts chemical energy into electrical energy whereas an electrolytic cell is one which converts electrical energy into chemical energy. Since batteries convert chemical energy to electrical energy, it is an arrangement of electrochemical cells.

2. Which of the following is not a requirement for a useful battery?
a) It should be light and compact
b) It should have a reasonable life span
c) It should ideally have a constant voltage throughout its lifespan
d) It should supply Alternating Current(AC)
Answer: d
Clarification: A useful battery is expected to be light and compact to be easily transported. It is expected to have a reasonable lifespan to justify its usage. Its voltage should not vary appreciably during usage so that it doesn’t adversely affect the circuit it is used in. A battery supplies Direct Current(DC) and not Alternating Current(AC).

3. Which of the following statements is true regarding a primary cell?
a) The electrode reactions can be reversed
b) It can be recharged
c) An example of a primary cell is a mercury cell
d) An example of a primary cell is a nickel-cadmium storage cell
Answer: c
Clarification: A primary cell is one in which the electrode reactions occur only once and cannot be reversed by applying electrical energy. Therefore, primary cells cannot be recharged. A mercury cell is an example of a primary cell, whereas a nickel-cadmium storage cell is an example of a secondary cell.

4. Secondary cells are also called storage cells.
a) True
b) False
Answer: a
Clarification: Secondary cells are those cells in which the electrode reaction can be reversed by applying an electrical energy. Therefore, they can be used to store electrical energy. So, they are also known as storage cells.

5. Which of the following is used as an anode in a dry cell?
a) Zinc
b) Graphite
c) Mercury(II) oxide
d) Nickel
Answer: c
Clarification: A dry cell is constructed using zinc and graphite. It consists of a zinc cylinder through whose centre passes a graphite rod. The zinc cylinder acts as an anode, whereas the graphite rod acts as a cathode.

6. Why do leak proof dry cells have an iron or steel sheet covering the zinc cylinder?
a) It increases the potential difference between the anode and cathode
b) It acts as a barrier around the zinc cylinder which can develop holes during use
c) It makes it waterproof
d) It prevents the leakage of current
Answer: b
Clarification: In a dry cell, zinc loses electrons and the zinc ions dissolve into the electrolyte. As a result, the zinc cylinder of the dry cell develops holes as it is used. To prevent the leakage of electrolyte through these holes, an iron or steel sheet is used to cover the cylinder.

7. Which of the following is the electrolyte used in a dry cell?
a) Ammonium chloride
b) Manganese dioxide
c) Potassium hydroxide
d) Sulphuric acid
Answer: a
Clarification: The electrolyte in a dry cell is ammonium chloride in the form of a moist paste placed next to the zinc anode. In some dry cells marketed as “heavy-duty”, the ammonium chloride is replaced by zinc chloride.

8. What is the role of manganese dioxide in a dry cell?
a) It acts as an electrolyte
b) It acts as the cathode
c) It acts as an anode
d) It acts as a depolariser
Answer: d
Clarification: In a dry cell, in the remaining space between the electrolyte and the graphite cathode, a second paste consisting of ammonium chloride and manganese dioxide is applied. The manganese dioxide acts as a depolariser as it helps to prevent the build-up of hydrogen gas bubbles.

9. What is the final oxidation state of manganese after the electrochemical reactions in a dry cell?
a) +4
b) +3
c) +2
d) +1
Answer: b
Clarification: In a dry cell, in the cathode reaction, manganese dioxide(MnO₂) is reduced to form manganese oxide-hydroxide(MnO(OH)). In this process, the oxidation state of manganese changes from +4 to +3. Hence the final oxidation state of manganese is +3.

10. Which of the following scientists invented the first dry cell?
a) Carl Gassner
b) Nikola Tesla
c) Antione Lavoisier
d) Georges Leclanché
Answer: a
Clarification: In the year 1886, Carl Gassner obtained a German patent on a variant of the wet Leclanché cell, which can be known as the dry cell because it did not have a liquid electrolyte. Instead, a mixture of ammonium chloride and plaster of paris was used.

11. What is the final product that zinc forms during the functioning of a mercury cell?
a) ZnO
b) ZnO₂
c) Zn
d) Zn(OH)₂
Answer: a
Clarification: A mercury cell consists of a zinc anode and a mercury(II) oxide cathode. Potassium hydroxide is used as the electrolyte. In the electrochemical reaction, zinc is oxidised to become zinc oxide(ZnO) whereas mercury(II) oxide is reduced to elemental mercury.

12. Which of the following appliances would not use sodium hydroxide as an electrolyte in their mercury cells?
a) Calculators
b) Hearing aids
c) Electronic watches
d) Photographic cameras with a flash
Answer: d
Clarification: Sodium hydroxide cells have nearly constant voltage at low discharge currents whereas potassium hydroxide cells provide a constant voltage at high discharge currents. Therefore, sodium hydroxide cells are ideal for calculators, hearing aids and electronic watches whereas potassium hydroxide cells are ideal for photographic cameras with a flash.

13. Which of the following is the voltage output of a mercury cell?
a) 1.55V
b) 1.35V
c) 2.55V
d) 1V
Answer: b
Clarification: Mercury batteries use a reaction between mercuric oxide and zinc in an alkaline electrolyte to produce electricity. Its voltage during discharge is a constant 1.35V. The common dry cell, on the other hand, provides a voltage of 1.5V.

14. Which of the following statements is not true with respect to a lead storage cell (or a lead-acid battery)?
a) The electrolyte used is an aqueous solution of sulphuric acid
b) The anode is made up of lead
c) The cathode is made up of lead(IV) oxide
d) It is a primary cell
Answer: d
Clarification: A lead storage cell is a secondary cell which has a grid of lead packed with finely divided spongy lead for an anode and a grid of lead packed with lead(IV) oxide for a cathode. The electrolytic solution used in a lead-acid battery is an aqueous solution of sulphuric acid.

15. Which of the following products are formed when a lead storage battery is discharged?
a) SO₂
b) Pb
c) PbO₂
d) PbSO₄
Answer: d
Clarification: During the working of the lead storage battery, PbSO₄ is formed at both the electrodes and sulphuric acid is used up. At the anode, Pb is oxidised to form PbSO₄ and at the cathode, PbO₂ is reduced to form PbSO₄.