PHOTOCHEMISTRY AND MOLECULAR SYMMETRY MCQs

By: Prof. Dr. Fazal Rehman | Last updated: May 29, 2025

1. : One mole of photon is called _____ .
(A) Quantum
(B) Energy Packet
(C) Einstein
(D) None of A, B, and C

2. : The emission of light in a biological reaction is called ___.
(A) Fluorescence
(B) Phosphorescence
(C) Chemiluminescence
(D) Bioluminescence

3. : “Only those radiations which are absorbed by the system can bring about chemical change”. This is a statement of the
(A) Beer-Lambert law
(B) Photochemical equivalence law
(C) Einstein law
(D) Grotthus-Draper law

4. : ____ is the glow of yellow phosphorous as a result of slow oxidation in air.
(A) Photolysis
(B) Luminescence
(C) Bioluminescence
(D) Chemiluminescence

5. : The spin multiplicity of the electronic state is equal to
(A) S+1
(B) 2S + 2
(C) 2S – 2
(D) 2S + 1

6. : Reactions in which molecules absorbing light do not themselves react but induce other molecules to react are called
(A) Chain reactions
(B) Free radical reactions
(C) Reversible reactions
(D) Photosensitized reactions

7. : A molecule returns from the excited singlet state to the ground singlet state with emission of light. This process is called _____.
(A) Phosphorescence
(B) Scattering
(C) Fluorescence
(D) Chemiluminescence

8. : Which statement is not true with respect to photochemical reactions?
(A) Temperature has significant effect on rate of these reactions
(B) Free energy of these reactions may be positive or negative
(C) Light intensity affects these reactions
(D) These take place in the presence of light

9. : Which statement is not related with high quantum yield reasons?
(A) The primary photochemical process may be reversed
(B) The active molecules may collide with other molecules and activate these molecules
(C) The reaction may be exothermic and heat evolve may activate other molecules
(D) Formation of reactive intermediates which may act as catalyst

10. : According to “The Lambert-Beer law”, ______
(A) Transmission is directly proportional to path length
(B) Transmission is directly proportional to concentration
(C) Absorbance is directly proportional to concentration & path length
(D) Absorbance is inversely proportional to transmission

11. : A molecule goes from the excited singlet to the triplet state without emitting light. The process is called _____.
(A) Inter-system crossing
(B) Phosphorescence
(C) Internal conversion
(D) Fluorescence

12. : When a transition occurs between states of the same multiplicity without emitting light, the process is called
(A) Fluorescence
(B) Quenching
(C) Intersystem crossing
(D) Internal conversion

13. : A molecule returns from the first excited triplet state to the ground singlet state. The light emitted is called _____.
(A) Inter-system crossing
(B) Phosphorescence
(C) Fluorescence
(D) Quenching

14. : The quantum yield of a photochemical reaction is
(A) Can have any value 0 depending on the reaction
(B) Forever equal to unity
(C) Forever greater than unity
(D) Forever less than unity

15. : Which reaction does not take place with light radiation?
(A) Double displacement
(B) Reduction
(C) Polymerization
(D) Oxidation

16. : Which radiations are photochemically active?
(A) Microwaves
(B) Radio waves
(C) Ultraviolet
(D) Infrared

17. : The wavelength of fluorescent light (λf) is related to the wavelength of absorbed light (λab) by

18. : The value of an Einstein
(A) Is independent of wavelength
(B) Depends on the temperature of the absorbing system
(C) Increases with increase in wavelength
(D) Decreases with increase in wavelength

19. : Ethylene belongs to
(A) C2v group
(B) D∞h group
(C) C2v group
(D) D2v group

20. : Which molecules have center of symmetry?
(A) H₂O
(B) HCl
(C) H₂SO₄
(D) CO₂

21. : According to the Grotthus-Draper law
(A) Only absorbed light is effective in producing photochemical changes
(B) Only light between certain wavelengths is effective in photochemical changes
(C) The light absorbed is proportional to its intensity
(D) Light is effective only for photochemical reactions in solution.

22. : Which molecules belong to C₃v point group?
(A) NH₃
(B) H₂S
(C) BF₃
(D) H₂O

23. : The branch of chemistry dealing with the study of reactions in the UV-visible region of the spectrum is called _____.
(A) Kinetics
(B) Cryoscopy
(C) Surface chemistry
(D) Photochemistry

24. : A line, a point or a plane about which a symmetry operation is performed, is called _____.
(A) Symmetry
(B) Symmetry operation
(C) Reflection
(D) Inversion element

25. : Which item is not a symmetry element?
(A) Optical activity
(B) Inversion center
(C) Improper rotation
(D) Plane of symmetry

26. : What is the reverse of a photochemical reaction?
(A) Phosphorescence
(B) Photosensitization
(C) Fluorescence
(D) Chemiluminescence

27. : Which symmetry element leaves the molecule or an object unchanged?
(A) Identity
(B) Improper rotation
(C) Inversion axis
(D) Proper rotation

28. : In proper rotation (Cn), an object is rotated through an angle of
(A) π/n radians
(B) 4π/n radians
(C) 3π/n radians
(D) 2π/n radians

29. : Which molecules possess a horizontal mirror plane?
(A) PF₃
(B) Water
(C) Ammonia
(D) H₂S

30. : What is the point group of CO₂?
(A) D6h
(B) C4v
(C) C6v
(D) D2h

31. : A photosensitizer is a substance that
(A) Initiates a photochemical reaction
(B) Decreases the speed of a chemical reaction
(C) Stops the photochemical reaction
(D) Increases the speed of a chemical reaction

32. : The extinction coefficient has the units
(A) cm³ mol⁻¹
(B) cm² mol⁻¹
(C) mol cm⁻²
(D) mol cm⁻³

33. : Which technique is helpful and used to study photochemical processes?
(A) Flash photolysis
(B) Dilatometry
(C) Viscometry
(D) Polarimetry

34. : CO belongs to which group?
(A) C2v
(B) D2h
(C) D∞h
(D) C∞v

35. : How many planes of symmetry are present in benzene?
(A) 6 planes
(B) 3 planes
(C) 5 planes
(D) 1 plane

36. : PF₅ belongs to which point group?
(A) D2h
(B) D4h
(C) D5h
(D) D3h

37. : The point group of XeOF₄ is
(A) C6v
(B) D2h
(C) D4h
(D) C4v

38. : What is the point group of BF₃?
(A) D3h
(B) C4v
(C) C3v
(D) D2h

39. : Linear molecules have ____ axis of rotation
(A) C∞
(B) C2
(C) C3
(D) C1

40. : In C-axis of rotation, an object is rotated through an angle of
(A) 90°
(B) 180°
(C) 100°
(D) 120°

41. : What is the point group of benzene?
(A) D6h
(B) C4v
(C) C6v
(D) D2h

42. : What is the point group of SF₆?
(A) C6v
(B) C4v
(C) Tetrahedral
(D) Octahedral

43. : Which is a non-radioactive relaxation process?
(A) Internal conversion
(B) Intersystem crossing
(C) Vibrational relaxation
(D) All of A, B, and C

44. : Which molecules have rotation-reflection axis?
(A) Methane
(B) Allenes
(C) Staggered ethene
(D) All of A, B, and C

45. : Which molecules belong to special point group D∞h?
(A) CO₂
(B) H₂
(C) Cl₂
(D) All of A, B, and C

46. : In a photochemical reaction
(A) ΔF is positive
(B) ΔF is negative
(C) ΔF is 0
(D) None of A, B, and C

47. : Which statement is not true with respect to group theory?
(A) Each group element has no reciprocal
(B) An element combines with itself to form another element of the group
(C) Each element of the group obeys associative law of combination
(D) Two elements of a group combine to form a third element of a group

48. : Which is a photochemical reaction?
(A) Photosynthesis
(B) Photography
(C) Vision reaction
(D) All of A, B, and C

49. : Which is not a component of laser?
(A) Photo detector
(B) Laser medium
(C) Optical resonator
(D) Energy source

50. : Which is a radioactive relaxation process?
(A) Internal conversion
(B) Phosphorescence
(C) Vibrational relaxation
(D) Intersystem crossing

51. : Which acts as a photosensitizer?
(A) Ni
(B) Cr
(C) Hemoglobin
(D) Chlorophyll

52. : Methane belongs to ______.
(A) D∞h
(B) Tetrahedral group
(C) C∞v
(D) Octahedral group