Category: Class 12 Chemistry Objective Questions

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.

Chemistry Multiple Choice Questions on “Concentration of Ores”.

1. Concentration of ores is also known as ore-dressing.
a) True
b) False
Answer: a
Clarification: The removal of unwanted earthy and silicious impurities (that is, gangue or matrix) from an ore is called concentration of ores. Concentration of ores is also known as ore-dressing.

2. Which of the cases is suitable for concentration by hand picking?
a) When either the ore or the impurities are magnetic
b) When the ore particles are heavier than the impurities
c) When the ores are good conductors of electricity
d) When the impurities can be distinguished from the ore by the naked eye
Answer: d
Clarification: In the case of concentration by hand picking, it is necessary that the impurities be easily distinguishable from the particles of the ore. Only if these impurities can be distinguished by the naked eye, is the ore said to be suitable for concentration by hand picking.

3. Which of the following equipment is used for concentration by hydraulic washing?
a) Stamp mill
b) Ball mill
c) Wilfley tables
d) Magnetic roller
Answer: c
Clarification: Hydraulic washing is usually used for concentration of ores when the particles of the ore have a higher mass compared to the earthy or rocky gangue particles. The process is carried out in specially designed tables called Wilfley tables.

4. Ores obtained from the Earth’s crust are always pure.
a) True
b) False
Answer: b
Clarification: Ores, as they are obtained from the Earth’s crust, are never pure. They are usually associated with earthy and silicious impurities (along with impurities of other minerals) called gangue or matrix.

5. Which of the following ores cannot be concentrated by hydraulic washing?
a) Haematite
b) Pyrolusite
c) Tinstone
d) Native ores of silver
Answer: b
Clarification: Concentration by hydraulic washing requires the ore particles to have a higher mass compared to its gangue particles. Hydraulic washing can be used for oxide ores of iron and tin such as haematite and tinstone and also for native ores of silver and gold. Pyrolusite is concentrated by magnetic separation.

6. Which of the following cannot be concentrated by electromagnetic separation?
a) Chromite
b) Magnetite
c) Pyrolusite
d) Zinc blende
Answer: d
Clarification: Electromagnetic separation is used to concentrate an ore when either the particles of the ore or the impurities present in it are magnetic in nature. Chromite, magnetite and pyrolusite have magnetic nature and are separated from their non-magnetic gangue particles using this method. Zinc blende is concentrated using electrostatic separation or froth floatation.

7. Where are the magnetic particles collected in concentration by electromagnetic separation?
a) Below the magnetic roller
b) Above the magnetic roller
c) Away from the magnetic roller
d) On the conveyer belt
Answer: a
Clarification: In electromagnetic separation, the powdered ore is dropped over a conveyer belt moving around two rollers, one of which has an electromagnet in it. As the ore particles roll over the belt, the magnetic particles are attracted by the magnetic roller. As a result, two heaps are formed separately. The heap collected below the magnetic roller contains magnetic particles while the heap away from the roller consists of non-magnetic particles.

8. What is the property of necessary for an ore to be concentrated by electrostatic separation?
a) The ore particles should be heavier than the gangue particles
b) The ore particles should be magnetic in nature
c) The ores should conduct electricity
d) It should be a sulphide ore
Answer: c
Clarification: Electrostatic separation is a method used for concentration or separation of ores when they are good conductors of electricity. It is based on the principle that when an electrostatic field is applied the ore particles, which conduct electricity, get charged and get repelled by electrodes having same charge and all thrown away.

9. Which of the following are collectors used in the froth floatation process?
a) Aniline
b) Pine oil
c) Ethyl xanthate
d) Potassium ethyl xanthates
Answer: a
Clarification: Froth floatation is generally used for sulphide ores. It is based on the fact that sulphide ores are preferentially wetted by oils while that of the gangue is wetted by water. To a suspension of the crushed ore in water, collectors are added to enhance the non-wettability of the ore particles. Pine oil, ethyl xanthate and potassium ethyl xanthates are examples of collectors.

10. What is the role of the rotating paddle in froth floatation?
a) Enhances wettability of gangue particles
b) Stabilizes the froth
c) Draws in air causing frothing
d) Enhances non-wettability of the ore particles
View Answer

Answer: c
Clarification: In froth floatation process, the suspension of the powdered ore in water along with the collectors and froth stabilizers is violently agitated by the rotating paddle which draws in air, causing frothing.

Chemistry Multiple Choice Questions on “P-Block – Group 16 Elements”.

1. Group 16 elements are also called Chalcogens.
a) True
b) False
View Answer

Answer: a
Clarification: Group 16 elements, also known as the Oxygen family, are also called Chalcogens (pronounced as kal’-ke-jens) (meaning ore forming elements) because many metals occur as oxides and sulphides.

2. Which of the following elements does not belong to group 16 of the periodic table?
a) Oxygen
b) Phosphorus
c) Sulphur
d) Selenium
Answer: b
Clarification: Group 16 of the periodic table consists of five elements viz., Oxygen (O), Sulphur (S), Selenium (Se), Tellurium (Te) and Polonium (Po). The elements of this group are commonly known as the oxygen family after the name of its first member.

3. Which is the most abundant group 16 element?
a) Oxygen
b) Sulphur
c) Selenium
d) Tellurium
Answer: a
Clarification: Oxygen is the most abundant of all elements. It occurs in the free state as dioxygen (O₂) and makes up 20.46% by volume and 23% by mass of the atmosphere. It also occurs in the form of ozone (O₃).

4. Ozone is an allotrope of Oxygen.
a) True
b) False
Answer: a
Clarification: Oxygen also occurs as ozone (O₃), an allotrope of oxygen, in the upper atmosphere which protects us from the harmful radiations of the sun. Ozone is a pale blue gas with a distinctively pungent smell.

5. What is the general outer electronic configuration of the Oxygen family?
a) ns²np⁴
b) ns²np³
c) ns²np⁵
d) ns²np²
Answer: a
Clarification: The elements of group 16 have six electrons in the valence shell and hence their general outer electronic configuration is ns²np⁴. The four p-electrons are arranged in three p-orbitals as p_x²p_y¹p_z¹ in accordance with Hund’s rule.

6. Which of the following statements regarding group 16 elements is not true?
a) The electronic configuration of Oxygen is [He]2s²2p⁴
b) The electronic configuration of Sulphur is [Ne]3s²3p⁴
c) The atomic radii of the elements of group 16 are larger than those of the corresponding elements of group 15
d) The electronic configuration of Tellurium is [Kr]4d¹⁰5s²5p⁴
Answer: c
Clarification: When you move across the periodic table, from left to right, the atomic size of the respective elements decreases due to increase in nuclear charge. Therefore, the atomic radii of the elements of group 16 are smaller than those of the corresponding elements of group 15.

7. Which group 16 element is the most electronegative?
a) Sulphur
b) Polonium
c) Oxygen
d) Selenium
Answer: c
Clarification: The elements of group 16 have higher values of electronegativity than the corresponding elements of group 15. Actually, oxygen is the second most electronegative element (EN=3.5), the first being fluorine (EN=4.0).

8. Which of the following is radioactive in nature?
a) Oxygen
b) Sulphur
c) Tellurium
d) Polonium
Answer: d
Clarification: Oxygen is the most non-metallic element of group 16. Sulphur is also a typical non-metal and Tellurium is a metalloid. Polonium is, however, metallic in nature but is radioactive with a short half-life (13.8 days).

9. Which of the following does not exist as an octatomic solid?
a) Sulphur
b) Tellurium
c) Selenium
d) Oxygen
Answer: d
Clarification: Oxygen exists as a diatomic gas at room temperature while other elements (S, Se and Te) exist as octatomic solids. Due to small size and high electronegativity, oxygen atom forms pπ – pπ double bond with other oxygen atom to form O = O molecule. The intermolecular forces of attraction between oxygen molecules are weak van der Waals forces and hence oxygen exists as a diatomic gas at room temperature.

10. Which group 16 element has the highest tendency for catenation?
a) Oxygen
b) Sulphur
c) Selenium
d) Polonium
Answer: b
Clarification: Sulphur has a stronger tendency for catenation than Oxygen. Due to small size, the lone pairs on the Oxygen atoms repel the bond pair of the O-O bond to a greater extent than the lone pairs of electrons on the Sulphur atoms in S-S bond. As a result, S-S bond is much stronger than O-O bond and hence Sulphur has a much stronger tendency for catenation than Oxygen.

11. Which group 16 element has 8 allotropic forms?
a) Sulphur
b) Oxygen
c) Selenium
d) Polonium
Answer: c
Clarification: Selenium has eight allotropic forms, of which three are red monoclinic forms containing Se₈ rings. The thermodynamically most stable form is grey hexagonal metallic Selenium which consists of polymeric helical chains.

12. What is the most reactive element of group 16?
a) Oxygen
b) Sulphur
c) Tellurium
d) Selenium
Answer: a
Clarification: Oxygen is the most reactive element of group 16. It is the second most electronegative element in the periodic table (EN=3.5), the first being fluorine (EN=4.0), making it more reactive than the other elements of the group.

13. Which of the following is a photosensitive element?
a) S
b) Se
c) O
d) Po
Answer: b
Clarification: The grey form of Selenium (metallic) and Tellurium consist of parallel chains held by weak metallic bonds. In the presence of light, the weak metallic bonds are excited and as a result, the number of free electrons increases and so does the conductivity. Thus, these elements conduct electricity significantly only in the presence of light. That is why Se and Te are called photosensitive elements.

14. What is the correct order of reactivity of group 16 elements?
a) O > Se > S > Te > Po
b) S > O > Te > Po > Se
c) S > O > Se > Te > Po
d) O > S > Se > Te > Po
Answer: d
Clarification: Oxygen is the most reactive group 16 element. Its reactivity is only slightly less than the most reactive elements, halogens. Sulphur is also very reactive particularly at high temperatures which helps in the cleavage of S-S bonds present in S₈ molecules. However, as we move down the group, the reactivity decreases, i.e., O > S > Se > Te > Po.

15. Which of the following is not poisonous?
a) H₂O
b) H₂S
c) H₂Se
d) H₂Te
Answer: a
Clarification: The hydride of Oxygen, i.e., H₂O is a colourless, odourless liquid while the hydrides of all the other group 16 elements are unpleasant, foul smelling, poisonous gases. H₂O has the highest boiling point of 373 K amongst the hydrides of group 16 elements.