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1. Nylon threads are made of
a.polyester polymer
b.polyamide polymer
c.polyethylene polymer
d.polyvinyl polymer
Answer: (b)

2. Which of the following is a branched polymer?
a.low density polymer
b.polyester
c.high density polymer
d.nylon
Answer: (a)

3. On the basis of mode of formation polymers can be classified:
a.as addition polymers only
b.as condensation polymers only
c.as copolymers
d.as addition and condensation polymers
Answer: (d)

4. The process of heat softening, moulding and cooling to rigidness can be repeated for which plastics?
a.thermoplastics
b.thermosetting plastics
c.both (a) and (b)
d.neither (a) nor (b)
Answer: (a)

5. The polymer used in making hair synthetic hair wigs is mage up of
a.CH2=CHCl
b.CH2=CHCOOCH3
c.C6H5CH=CH2
d.CH2=CH-CH=CH2
Answer: (a)

6. Which of the following monomers form biodegradable polymers?
a.3-hydroxybutanoic acid + 3-hydroxypentanoic acid
b.Glycine + amino caproic acid
c.ethylene glycol + phthalic acid
d.both a and b
Answer: (d)

7. In addition polymer, monomer used is
a.unsaturated compounds
b.saturated compounds
c.bifunctional saturated compounds
d.trifunctional saturated compounds
Answer: (a)

8. Polymer formation from monomer starts by
a.the condensation reaction between monomers
b.the coordinate reaction between monomers
c.conversion of monomer to monomer ions by protons
d.hydrolysis of monomers
Answer: (a)

9. Which of the following statements is not correct for fibres?
a.Fibres possess high tensile strength and high modulus
b.Fibres impart crystalline nature
c.Characteristic features of fibres are due to strong intermolecular forces like hydrogen bonding
d.All are correct
Answer: (d)

10. Which of the following does not undergo additional polymerization?
a.vinyl chloride
b.butadiene
c.styrene
d.all of the above undergoes addition polymerizations
Answer: (d)

11. The polymers are classified into _________ types based on the nature of polymerization.
a) 5
b) 2
c) 3
d) 4
Answer: b
Explanation: The polymers are classified into two types based upon their nature of polymerization. They are homopolymers and co polymers.

12. A straight chain polymer comes under the _________ type of the polymers.
a) Homo polymers
b) Co-polymers
c) Regular chain copolymers
d) Irregular straight chain copolymers
Answer: a
Explanation: The straight chain polymers come under the homo polymers. The regular straight chain copolymers and irregular straight chain copolymer comes under the straight chain copolymers.

13. The different monomers are arranged alternatively in __________
a) Alternate straight chain polymers
b) Regular straight chain copolymers
c) Straight chain copolymer
d) Cross linked polymers
Answer: a
Explanation: The different monomers are arranged alternatively in alternate straight chain polymers. The regular straight chain polymers the monomeric units arranged regularly.

14. The polymers whose backbone is made of same type of atoms called ___________
a) Homo polymers
b) Heterochain polymers
c) Isotactic polymers
d) Atactic polymers
Answer: a
Explanation: The polymers whose back bone is made of some type of atoms is called as homopolymers. The heteropolymers backbone is constructed by the two or more than two different types of atoms.

15. Tacticity of the polymers is the arrangement of the ___________ on carbon backbone.
a) Hydrogen atoms
b) Nitrogen atoms
c) Functional groups
d) Carbons
Answer: c
Explanation: The tacticity is defined as the arrangement of the function groups on the carbon back bone of the polymer is called tacticity of the polymer.

16. Based on tacticity, the polymers are divided into __________ types.
a) Two
b) Three
c) Four
d) Five
Answer: b
Explanation: Based on tacticity, the polymers are divided into three types. They are Isotactic polymers, Atactic polymers and syndiotactic polymer.

17. The functional group are arranged on the same side of the carbon back bone are said to be _________
a) Syndiotactic polymers
b) Atactic polymers
c) Isotactic polymers
d) Chain polymers
Answer: c
Explanation: The functional groups arranged on the same side of the carbon back bone then it is isotactic polymer, if they no regular arrangement then they are said to be Atactic polymers.

18. Which of the following is the example of the syndiotactic polymers?
a) Poly propylene
b) Poly vinyl chloride
c) Gutta percha
d) Poly lactic acids
Answer: c
Explanation: The gutta percha is the natural form of rubber. It is the example of the syndiotactic polymers in which the functional groups are alternately arranged. Poly propylene and poly lactic acids are the examples of the isotactic polymers.

19. Alternate straight chain polymers are ___________
a) Soft and flexible
b) Hard and flexible
c) Soft and brittle
d) Hard and brittle
Answer: a
Explanation: Alternate straight chain polymers are soft and brittle nature. All the straight chain polymers are soft and brittle.

20. Combination of the organic and inorganic polymers are called _________
a) Element organic polymers
b) Inorganic polymers
c) Fibres
d) Thermoplastics
Answer: a
Explanation: Combination of the organic and the inorganic polymers are called as the element of organic polymers. It comes under the synthetic polymers because it is produced by the synthesis.

21. Polymeric molecules __________ a definite crystalline structure.
a) Have
b) Do not have
c) Completely having
d) Partially having
Answer: b
Explanation: The polymeric molecules do not have a definite crystalline structure. The non-polymeric molecules have a definite crystalline structure.

22. The polymer is 100% crystalline.
a) True
b) False
Answer: b
Explanation: No polymer is 100% crystalline or 100% amorphous. A polymer is a mixture of 60% crystalline and 40% amorphous.

23. As the crystallinity increases The brittleness of the polymer _________
a) Increases
b) Decreases
c) Moderate
d) Remains constant
Answer: b
Explanation: As the crystallinity of the polymer increases then the brittleness of the polymer also increases. The strength and chemical resistance of the polymers also increases.

24. A polymeric molecules possess the molecular weight _____________
a) Different
b) Fixed
c) That cannot be determined
d) May be determined
Answer: a
Explanation: When polymerisation takes place, the growing polymeric chains are terminated at different sizes of molecules. So, as a result the polymeric molecules have different molecular weights.

25. Weight average molecular weight __________ on the weight of molecules in a polymer.
a) Dependent
b) Independent
c) Partially dependent
d) Neither dependent nor independent
Answer: a
Explanation: Weight average molecular weight depends on the weight of the molecules of each type and determined by making use of colloidal properties.

26. The polymer absorbs ________ and swells in size.
a) Ethyl alcohol
b) Ether
c) Water
d) Methanol
Answer: c
Explanation: The polymer absorbs the water and swells in size. Slowly polymer goes into the solution viscous polymer solution which is heterogeneous.

27. ___________ is the property of recovering original shape after the removal of deforming strain.
a) Rigidity modulus
b) Youngs modulus
c) Elasticity
d) Bulk modulus
Answer: c
Explanation: The elasticity is the property of recovering the original shape after removal of deforming strain. Natural rubber possess high elasticity due to the coiled helix structure of poly isoprene.

28. The impact strength is measured as _________
a) Elasticity
b) Strength
c) Permeability
d) Toughness
Answer: d
Explanation: The impact strength is measured as the toughness. Below the glass transition temperature, the polymers break.

29. If the polymer is in the room temperature then it is ___________
a) Brittle
b) Viscofluid state
c) Amorphous
d) Rubbery
Answer: d
Explanation: The effect of heat on polymer is high. If the temperature changes, the state of the polymer will be changed.

30. The strength of the polymer increases with ________ in molecular weight.
a) Increase
b) Decrease
c) No change
d) Slightly decrease
Answer: a
Explanation: The strength of the polymer increases with an increase in the molecular weight. The inter molecular attraction, presence of polar groups and chain length increases the strength.

31. Mechanism of polymerisation is classified into _______ types.
a) Two
b) Three
c) Four
d) Five
Answer: a
Explanation: Mechanism of polymerisation is classified into two types. They are chain or addition polymerisation and the step or condensation polymerisation.

32. The functionality of the monomer is a __________ bond.
a) Single
b) Double
c) Triple
d) No
Answer: b
Explanation: The functionality of the monomer is a double bond and bi functional. The chain polymerisation yields the product which is exact multiple of the monomers.

33. The polymerisation takes place by __________ of the monomer molecules.
a) Addition
b) Self addition
c) Dissociation
d) Condensation
Answer: b
Explanation: The polymerisation takes place by self addition of the monomer molecules to each other through the chain polymerisation.

34. The bi products like water, methyl alcohol are produced in chain reaction.
a) True
b) False
Answer: b
Explanation: The bi products like water, methyl alcohol are not produced in the chain reaction. The polymer has the same chemical composition as that of the monomer in chain polymerisation.

35. In how many steps the mechanism of the chain polymerisation is carried out?
a) Two
b) Three
c) Four
d) Five
Answer: b
Explanation: The mechanism of the chain polymerisation is carried out in three steps. They are 1. initiation, 2. propagation and 3. termination.

36. The chain polymerisation mechanism is _______
a) Slow
b) Very slow
c) Rapid
d) Moderate
Answer: c
Explanation: The chain polymerisation mechanism is rapid. An initiator is required to start the polymerisation reaction.

37. The conversion of pi-bond to sigma bond during the chain propagation releases the energy of _________ K.cal/mole.
a) 10
b) 30
c) 40
d) 20
Answer: d
Explanation: The conversion of the pi-bond into the sigma bond during the chain polymerisation releases the energy of the 20K.cal/mole. An initiator is needed to start the polymerisation reaction.

38. Which of the following do not undergo the chain polymerisation?
a) Polyester
b) Vinyl
c) Allyl
d) Dienes
Answer: a
Explanation: The polyester do not undergo the chain polymerisation. The compounds having the double bond undergo chain polymerisation. Olefins, vinyl, allyl and dienes undergo chain polymerisation.

39. Addition polymerisation can be carried out in _________ mechanisms.
a) Two
b) Three
c) Four
d) Five
Answer: b
Explanation: Addition polymerisation can be carried out in three mechanisms. They are: 1 – free radical mechanism, 2 – ionic mechanism, 3 – co-ordination mechanism.

40. Initiators are __________ compounds.
a) Stable
b) Unstable
c) Partially stable
d) Highly stable
Answer: b
Explanation: Initiators are the unstable compounds. For getting stability, they undergo homolytic fusion to produce free radicals.

41. For free radical chain polymerisation _________ are the good initiators.
a) Benzoyl peroxide
b) Hydrogen peroxide
c) Benzoyl peroxide and hydrogen peroxide
d) Neither benzoyl peroxide nor hydrogen peroxide
Answer: c
Explanation: For free radical chain polymerisation, Benzoyl peroxide and hydrogen peroxide are the good initiators. They produce monomer free radicals.

42. The ionic mechanism again divided into _____________
a) Two
b) Three
c) Four
d) Five
Answer: a
Explanation: The ionic mechanism is again dividing into two types. They are: cationic chain polymerisation and anionic chain polymerisation.

43. The __________ of the inhibitor result in the cationic chain polymerisation.
a) Homolytic fusion
b) Partially homolytic fusion
c) Heterolytic fusion
d) Partially heterolytic fusion
Answer: c
Explanation: The heterolytic fusion of the initiator results in the cationic chain polymerisation and homolytic fusion results in a free radical polymerisation.

44. The anion is produced by the __________ initiates the anionic chain polymerisation.
a) Homolytic fusion of initiator
b) Heterolytic fusion of initiator
c) Organo-alkali compounds
d) Inorganic compounds
Answer: c
Explanation: The anion is produced by the organo-alkali compounds like ethyl sodium, methyl potassium, butyl lithium etc initiates the anionic chain polymerisation.

45. The catalyst used in the co-ordination polymerisation is __________
a) Ziegler-natta catalyst
b) Vanadium pent-oxide
c) Nitric oxide
d) Zeonar
Answer: a
Explanation: The catalyst used in the co-ordination polymerisation is Ziegler-natta catalyst. Combination of the metal halides and organometallic compounds are called as Ziegler-natta catalyst.

47. Polyethylene is a ___________
a) Bad conductor
b) Transparent
c) Polar material
d) High symmetrical structure
Answer: d
Explanation: Polyethylene is a rigid, waxy white, translucent, non-polar material, with high symmetrical structure. It is a good electrical insulator.

48. Which of the following is attacks the polyethylene?
a) Kerosene
b) Strong acids
c) Alkalis
d) Salt solutions
Answer: a
Explanation: The polyethylene is resistant to strong acids, alkalis and salt solutions. It is attacked by the oils and organic solvents. It is also resistant to oxygen, carbondioxide.

49. The low density polyethylene has a melting point.
a) 840C
b) 850C
c) 860C
d) 870C
Answer: d
Explanation: The low density polyethylene possess branched chain structure and its melting point is about the 870C.

50. Poly vinyl chloride is produced by the free radical chain polymerisation of the vinyl chloride in presence of the benzoyl peroxide.
a) True
b) False
Answer: a
Explanation: Poly vinyl chloride is produced by the free radical chain polymerisation of the vinyl chloride in presence of the benzoyl peroxide. The hydrogen peroxide can also be used as the catalyst instead of the benzoyl peroxide.

51. Poly vinyl chloride is a __________
a) Blue coloured compound
b) Inflammable
c) Weak
d) Brittle
Answer: d
Explanation: Poly vinyl chloride is a colourless, non-inflammable and chemically inert in nature. It is strong and brittle.

52. Plasticized poly vinyl chloride can be used for _________
a) High frequency insulator parts
b) Bottle caps
c) Coated wires
d) Electrical insulation
Answer: d
Explanation: Plasticized poly vinyl chloride can be used for electrical insulation, injection moulding articles like tool handles, radio and telephone components.

53. Phenol is made to react with formaldehyde in the presence of acid or alkali produces ________
a) Phenol
b) Poly vinyl chloride
c) Plasticized poly vinyl chloride
d) Polyethylene
Answer: a
Explanation: Phenol is made to react with formaldehyde in the presence of acid or alkali produces di, tri and mono phenols depending on the phenol formaldehyde ratio.

54. Bakelite is __________
a) Good anion exchanging resin
b) Attacked by acids
c) Attacked by salts
d) Resistant to alkalis
Answer: a
Explanation: Bakelite is a good anionic exchanging resin. It is a good adhesive and it is resistant to acids and salts. It is attacked by the alkalis.

55. Glass laminates can be made by using ___________
a) Poly vinyl chloride
b) Bakelite
c) Polyethylene
d) Phenol
Answer: b
Explanation: Glass laminates can be made by using Bakelite. Bakelite is also called as the phenol-formaldehyde resin.

56. Bakelite is not _______
a) Hard
b) Strong
c) Rigid
d) Weak
Answer: d
Explanation: Bakelite is not weak. It is hard, strong and rigid. It is an excellent electrical insulator. It is scratch resistant and water resistant.

57. The bearings used in the propeller shafts are prepared using ________
a) Phenol-formaldehyde resin
b) TEFLON
c) Vinyl cyanide
d) Vinyl iso cyanide
Answer: a
Explanation: The bearings used in the propeller shafts are made by using Phenol-formaldehyde resin. It is also used in the paper industry and rolling mills.

58. TEFLON is obtained by the chain polymerisation of tetra fluoro ethylene in presence of __________ as initiator.
a) Hydrogen peroxide
b) Hydrogen nitrate
c) Hydrogen
d) Benzoyl peroxide
Answer: d
Explanation: TEFLON is obtained by the chain polymerisation of the tetra fluoro ethylene in presence of the benzoyl peroxide as an initiator.

59. TEFLON has _________
a) High melting point
b) Low melting point
c) Low density
d) Good conduction of electricity
Answer: a
Explanation: TEFLON has a high melting point, high density and it is the bad conductor of electricity as it is an insulator.

60. TEFLON is used to make chemical carry pipes due to its __________
a) extreme chemical resistance
b) Resistance towards alkalis
c) Resistance towards strong acids
d) Resistance towards salts
Answer: a
Explanation: TEFLON is used to make chemical carry pipes due to its extreme chemical resistance. It is used for making the gaskets, pump parts, tank linings and tubing.

Applied Chemistry

1. Which of the following defines the Mass number of an atom?
a.number of protons + number of electrons
b.number of neutrons + number of electrons
c.number of protons + number of neutrons
d.number of electrons
Answer (c). number of protons + number of electrons

2. Who is credited with the discovery of electron?
a.JJ Thomson
b.James Chadwick
c.Ernest Rutherford
d.Niels Bohr
Answer (a). JJ Thomson

3. An atom has a mass number of 37 and atomic number 17. How many protons does it have?
a.20
b.17
c.54
d.21
Answer (b). 17

4. Which of the following mostly accounts for the mass of an atom?
a.neutrons
b.neutron and proton
c.electron and proton
d.electron and neutron
Answer (b).

5. Within an atom, the nucleus when compared to the extra nuclear part is
a.bigger in volume and heavier in mass
b.smaller in volume but heavier in mass
c.smaller in volume and lighter in mass
d.same size
Answer (b). smaller in volume but heavier in mass

6. What would be the atomic number of the element in whose atom the K and L shells are full?
a.10
b.12
c.14
d.16
Answer (a). 10

7. Which metal was used by Rutherford in his alpha-scattering experiment?
a.gold
b.platinum
c.silver
d.lead
Answer (a). gold

8. An element has an electronic configuration of 2, 8, 7. Its valency is
a.2
b.7
c.3
d.1
Answer (d). 1

9. During a chemical reaction, atomic number
a.changes
b.remains same
c.changes and then is restored
d.changes alternately
Answer (b). remains same

10. Which isotope of hydrogen contains only one proton and no neutron in its nucleus?
a.protium
b.deuterium
c.tritium
d.None of the above
Answer (a). protium

11. Who of the following was awarded the Nobel Prize for his measurement of elementary electronic charge?
a.Rutherford
b.Robert Millikan
c.James Chadwick
d.JJ Thomson
Answer (b). Robert Millikan

12. How are the subshells in an atom labelled?
a.s, p, d, f, g
b.s, p, f, g, d
c.s, f, g, d, f
d.s, d, g, p, f
Answer (a). s, p, d, f, g

13. The isotopes of neutral atoms of an element differ in
a.Atomic number
b.Mass number
c.Number of electrons
d.Chemical properties
Answer (b). Mass number

14. The electronic configuration of an atom having atomic number 20 is
a.2, 8, 8, 2
b.2, 8, 10
c.2, 6, 8, 4
d.2, 4, 8, 6
Answer (a). 2, 8, 8, 2

15. Almost the entire mass of an atom is concentrated in the
a.proton
b.electrons
c.nucleus
d.neutrons
Answer (c). nucleus

16. An atom differs from its ion in
a.Nuclear charge
b.Mass number
c.Number of electrons
d.Number of neutrons
Answer (c). Number of electrons

17. The proton is heavier than an electron by
a.187 times
b.1837 times
c.3837 times
d.2827 times
Answer (b). 1837 times

18. Which of the following is true about a charged atom?
a.anion is negatively charged
b.cation is negatively charged
c.cation has gained an electrond.
anion has lost an electron
Answer (a).a.anion is negatively charged

19. Which of the following is not a fundamental particle?
a.Proton
b.Neut0ron
c.Alpha particle
d.Electron
Answer (c). Alpha particle

20. Which one among the following most correctly determines the atomic number of an element?
a. Number of protons
b. Number of protons and electrons
c. Number of ions
d. Number of nucleons
Answer (a). Number of protons

21. How many electrons does the outermost shell of neon have?
a. 4
b. 8
c. 2
d. 16
Answer (b). 8

23. Which of the following determines the chemical properties of an element?
a. Number of electrons
b. Number of neutrons
c. Number of protons
d. All of the above
Answer (a). Number of electrons

24. The number of protons in a negatively charged atom (anion) is
a. more than the atomic number of the element
b. less than the atomic number of the element
c. more than the number of electrons in the atom
d. less than the number of electrons in the atom
Answer (d). less than the number of electrons in the atom

25. Atoms which have same mass number but different atomic number are called
a. isotopes
b. isomers
c. isotones
d. isobars
Answer (d). isobars

26. The atomic theory of matter was first proposed by
a. John Dalton
b. Rutherford
c. J. J. Thomson
d. Niels Bohr
Answer (a). John Dalton

27. How many orbitals can have the following set of quantum numbers, n = 3, l = 1, m1 = 0 ?
a) 3
b) 1
c) 4
d) 2
Answer: (b). 1

28. Electronic configuration of the outer shell of the element Gd with atomic number 64 is
a) 4f4 5d5 6s1
b) 4f3 5d5 6s2
c) 4f5 5d4 6s1
d) 4f7 5d1 6s2
Answer: (d). 4f7 5d1 6s2

29. Maximum number of electrons in a subshell can be
a) 4l + 2
b) 4l – 2
c) 2n2
d) 2l + 1
Answer: (a). 4l + 2

30. The orientation of atomic orbitals depends on their
a) spin quantum number
b) magnetic quantum number
c) azimuthal quantum number
d) principal quantum number
Answer: (b). magnetic quantum number

31. A gas X has Cp and Cratio as 1.4, at NTP 11.2 L of gas X will contain_______ number of atoms
a) 1.2 × 1023
b) 3.01 × 1023
c) 2.01 × 1023
d) 6.02 × 1023
Answer: (d)

32. Number of unpaired electrons in N2+
a) 3
b) 1
c) 2
d) 0
Answer: (b). 1

33. The excitation energy of a hydrogen atom from its ground state to its third excited state is
a) 12.75 eV
b) 0.85 eV
c) 10.2 eV
d) 12.1 eV
Answer: (a). 12.75 eV

34. 3p orbital has _____ radial nodes
a) three
b) two
c) one
d) none
Answer: (c). one

35. A 0.66 kg ball is moving with a speed of 100 m/s. Find its wavelength
a) 6.6 × 10-34 m
b) 6.6 × 10-32 m
c) 1.0 × 10-32 m
d) 1.0 × 10-35 m
Answer: (d). 1.0 × 10-35 m

36. Which among the following has the shortest C-C bond length?
a) Ethene
b) Ethane
c) Benzene
d) Ethyne
Answer: (d). Ethyne

37. The oxygen molecule is paramagnetic. It can be explained by
a) Resonance
b) Hybridisation
c) Valence bond theory
d) Molecular orbital theory
Answer: (d). Molecular orbital theory

38. Find the paramagnetic species
a) CN
b) NO+
c) CO
d) O2
Answer: (d). O2

39. Find the diamagnetic species
a) H2
b) H2
c) He2+
d) H2+
Answer: (a). H2

40. Which of the following pairs has the same bond order?
a) O2+, NO+
b) N2, O2
c) O22-, B2
d) NO, CO
Answer: (c). O22-, B2

41. Each P of P4O10 is attached to how many oxygen atoms?
a) 3
b) 2.5
c) 2
d) 4
Answer: (d). 4

42. When O2 changes to O2, the electron goes to which of the orbitals?
a) 𝜋 orbital
b) 𝜎 orbital
c) 𝜋* orbital
d) 𝜎* orbital
Answer: (c). 𝜋* orbital

43. O-O bond length is minimum in
a) O2
b) O2
c) O2+
d) O22-
Answer: (c). O2+

44. Which of the following is not paramagnetic?
a) CO
b) N2+
c) NO
d) O2
Answer: (a). CO

45. Find the molecule having the highest bond order
a) O2+
b) O2
c) O22-
d) O2
Answer: (a). O2+

46. C-O bond length is minimum in
a) CO2
b) CO32-
c) HCOO
d) CO
Answer: (d). CO

47. Molecules are held together in a crystal by
a) hydrogen bond
b) electrostatic attraction
c) Van der Waal’s attraction
d) dipole-dipole attraction
Answer: (c). Van der Waal’s attraction

48. Sp3d2 hybridization is present in [Co(NH3)63+], find its geometry
a) octahedral geometry
b) square planar geometry
c) tetragonal geometry
d) tetrahedral geometry
Answer: (a). octahedral geometry

49. Find the molecule with the maximum dipole moment
a) CH4
b) NH3
c) CO2
d) NF3
Answer: (b). NH3

50. MX6 is a molecule with octahedral geometry. How many X – M – X bonds are at 180°?
a) four
b) two
c) three
d) six
Answer: (c). three

51. Find the pair with sphybridisation of the central molecule
a) NH3 and NO2
b) BF3 and NH2
c) BF3 and NO2
d) NH2– and H2O
Answer: (c). BF3 and NO2

52. The formal charge and P-O bond order in PO43- respectively are
a) 0.6, -0.75
b) -0.75, 1.25
c) 1.0, -0.75
d) 1.25, -3
Answer: (b). -0.75, 1.25

53. Which of the molecules does not have a permanent dipole moment?
a) SO3
b) SO2
c) H2S
d) CS2
Answer: (d). CS2

54. pℼ – dℼ bonding is present in which molecule
a) SO32-
b) CO32-
c) NO3
d) BO33-
Answer: (a). SO32-

55. Which one has a pyramidal shape?
a) SO3
b) PCl3
c) CO32-
d) NO3
Answer: (b). PCl3