SPECTROSCOPY MCQs

By: Prof. Dr. Fazal Rehman | Last updated: April 16, 2025

1. Which radiation has valence electron transitions?
(A) Microwave
(B) X-rays
(C) γ-rays
(D) Visible

2. The difference between the incident and scattered frequencies in the Raman spectrum is called the:
(A) Raman frequency
(B) Anti-Stokes line
(C) Stokes line
(D) P-branch

3. How many normal modes of vibration are possible for a CO₂ molecule?
(A) 4
(B) 2
(C) 3
(D) 1

4. The commonly used units for wavelength are:
(A) Centimeter
(B) Micrometer
(C) Nanometer
(D) All of the above

5. The degree of freedom for stretching motion in non-linear (acyclic) molecules is:
(A) N – 1
(B) N – 5
(C) N – 2
(D) N – 4

6. Which radiation has high energy?
(A) Radio waves
(B) Microwaves
(C) Visible
(D) Ultraviolet

7. Which radiation has the highest frequency?
(A) γ-rays
(B) Microwaves
(C) Infrared
(D) Radio waves

8. Which radiation is associated with rotational transitions?
(A) Microwave
(B) Infrared
(C) X-rays
(D) Visible

9. Which radiation is associated with vibrational transitions?
(A) Infrared
(B) γ-rays
(C) Microwave
(D) X-rays

10. Which molecule is not a symmetric top?
(A) H₂O
(B) BCl₃
(C) CH₃Cl
(D) BF₃

11. When all three principal moments of inertia of a molecule are equal, it is called a:
(A) Symmetric top
(B) Prolate symmetric top
(C) Asymmetric top
(D) Spherical top

12. Which information is obtained from the rotational spectra of a molecule?
(A) Molecular structure
(B) Dipole moment
(C) Atomic mass
(D) All of the above

13. Which technique is useful for functional group identification?
(A) FTIR spectroscopy
(B) Electronic spectroscopy
(C) NMR spectroscopy
(D) Rotational spectroscopy

14. The source of radiation in rotational spectroscopy is:
(A) Klystron valve
(B) Deuterium lamp
(C) Sodium lamp
(D) Tungsten lamp

15. Rotational spectra are observed in which region?
(A) Near infrared region
(B) Ultraviolet region
(C) Visible region
(D) Far infrared region

16. Which relationship is true regarding molecular energy levels?
17. The selection rule for the transition in rotational energy levels in the Raman spectrum is:
(A) ∆J = ±2
(B) ∆J = +1
(C) ∆J = +2
(D) ∆J = ±1

18. Which radiation has a longer wavelength?
(A) Radio wave
(B) Ultraviolet
(C) Microwave
(D) Gamma rays

19. What types of energy are possessed by molecules in the gaseous state?
(A) Translational energy
(B) Vibrational energy
(C) Rotational energy
(D) All of the above

20. Which molecule is inactive?
(A) N₂
(B) CO
(C) H₂O
(D) HC ≡ CH

21. How many normal modes of vibration are possible for the NH₃ molecule?
(A) 6
(B) 3
(C) 4
(D) 2

22. Which molecules do not show microwave spectrum?
(A) Spherical tops
(B) Symmetric tops
(C) Linear molecules
(D) Asymmetric tops

23. The range of the fingerprint region in IR spectroscopy is:
(A) 4000-600 cm⁻¹
(B) 4000-1450 cm⁻¹
(C) 1450-500 cm⁻¹
(D) None of the above

24. What is the source of light in IR spectroscopy?
(A) Nernst filament
(B) Tungsten lamp
(C) Electron beam
(D) Deuterium lamp

25. The detector used in IR spectroscopy is:
(A) Photocell
(B) Bolometer
(C) UV detector
(D) None of the above

26. The energy associated with a photon of light is ______:
(A) c = vλ
(B) E = hc
(C) E = mc²
(D) E = hu

27. The prism/monochromator used in spectroscopy is made of:
(A) KBr
(B) KCl
(C) CsCl
(D) CaCl₂

28. The selection rule for transitions in vibrational energy levels in the IR spectrum is:
(A) ∆v = ±4
(B) ∆v = ±2
(C) ∆v = ±3
(D) ∆v = ±1

29. Which of the following spectra arises when an electron jumps from one energy level to another?
(A) Electronic
(B) Vibrational
(C) Nuclear
(D) Rotational

30. Normally, the sample in rotational spectroscopy is in the form of:
(A) Gas
(B) Liquid
(C) Solid
(D) None of the above

31. Rotational spectroscopy cannot be applied to detect:
(A) Moment of inertia
(B) Interstellar space
(C) Molecular groupings
(D) Bond length

32. Which diatomic molecules will not give a rotational spectrum?
(A) N₂
(B) HF
(C) NO
(D) CO

33. The selection rule for transitions in rotational energy levels of a diatomic molecule is:
(A) ∆J = +1
(B) ∆J = -1
(C) ∆J = ±2
(D) ∆J = ±1

34. The vibrational degree of freedom for linear molecules is:
(A) 3N-5
(B) 3N-4
(C) 3N-6
(D) None of the above

35. What is the degree of freedom for bending motion for non-linear molecules?
(A) 2N-4
(B) 2N-1
(C) 2N-2
(D) 2N-5

36. What is the degree of freedom for bending motion for linear molecules?
(A) 2N-1
(B) 2N-5
(C) 2N-2
(D) 2N-4

37. In vibrational spectroscopy, the first overtone occurs at:
(A) 2V₁
(B) 4V₁
(C) 3V₁
(D) None of the above

38. In vibrational spectroscopy, the second overtone occurs at:
(A) 2V₁
(B) 4V₁
(C) 3V₁
(D) None of the above

39. Which bands arise simply from the addition of two or more fundamentals or overtones in IR?
(A) Overtones
(B) Difference band
(C) Addition bands
(D) Subtraction bands

40. Which is not an addition band?
(A) V₁ – V₂
(B) 2V₁ + V₂
(C) V₁ + V₂ + V₃
(D) V₁ + V₂

41. The vibrational degree of freedom for non-linear molecules is:
(A) 3N-6
(B) 3N-5
(C) 3N-4
(D) None of the above

42. When two vibrational frequencies resonate and exchange energy, the phenomenon is called:
(A) Fermi-resonance
(B) Stark effect
(C) Conjugation
(D) Zeeman effect

43. Which is true about skeletal vibrations?
(A) They usually fall in the range of 1400-700 cm⁻¹
(B) They arise from linear structures
(C) They arise from branched chain structures
(D) All of the above

44. The detector used in rotational spectroscopy is:
(A) Photocell
(B) Conductivity detector
(C) Radio receiver
(D) Bolometer

45. The range of the functional group region in IR spectroscopy is:
(A) 4000-1450 cm⁻¹
(B) 2000-500 cm⁻¹
(C) 4000-600 cm⁻¹
(D) None of the above