Molecular Spectroscopy and Molecularity of a Reaction MCQs

1. What does Molecular Spectroscopy mainly study?

(A) Colour of solids

(B) Motion of planets

(C) Nuclear fission

(D) Interaction of molecules with electromagnetic radiation

2. Molecularity of a reaction refers to:

(A) Number of moles of catalyst used

(B) Number of reacting species in an elementary step

(C) Mechanism steps

(D) Temperature change during reaction

3. Which type of spectroscopy deals with rotational transitions?

(A) NMR

(B) Microwave spectroscopy

(C) UV-Visible spectroscopy

(D) Raman spectroscopy

4. A unimolecular reaction involves:

(A) One molecule

(B) Two molecules

(C) Three molecules

(D) Four molecules

5. IR (Infrared) spectroscopy is mainly used to study:

(A) Vibrational transitions

(B) Rotational transitions

(C) Electronic transitions

(D) Nuclear transitions

6. A bimolecular reaction occurs when:

(A) Catalyst activates the reaction

(B) One species decays

(C) Two species collide

(D) Three species combine

7. UV-Visible spectroscopy detects:

(A) Vibrations of bonds

(B) Nuclear spin

(C) Neutron absorption

(D) Electronic transitions

8. Termolecular reactions are rare because:

(A) Probability of three-body collision is low

(B) Molecules do not collide

(C) Reactions occur only in solids

(D) They require catalysts

9. Which spectroscopy uses radiofrequency radiation?

(A) IR spectroscopy

(B) NMR spectroscopy

(C) UV-Visible spectroscopy

(D) X-ray spectroscopy

10. Molecularity applies only to:

(A) Overall reactions

(B) Complex reactions

(C) Reversible reactions

(D) Elementary reactions

11. Raman spectroscopy is based on:

(A) Scattering of light

(B) Absorption of microwaves

(C) Emission of UV light

(D) Nuclear spin flips

12. A reaction with molecularity of 3 is called:

(A) Unimolecular

(B) Termolecular

(C) Bimolecular

(D) Macromolecular

13. Beer–Lambert Law is applied in which spectroscopy?

(A) Microwave

(B) NMR

(C) UV-Visible

(D) IR

14. Molecularity can never be:

(A) Fractional

(B) A whole number

(C) Zero

(D) Three

15. IR absorption occurs when:

(A) Molecule changes orientation

(B) Electrons move to higher orbitals

(C) Dipole moment changes

(D) Nucleus vibrates

16. A reaction step involving two molecules has order:
(Order ≠ molecularity)

(A) Cannot be predicted

(B) One

(C) Two

(D) Zero

17. Which region is used for vibrational frequencies?

(A) X-ray

(B) Radiofrequency

(C) Visible light

(D) Infrared

18. Molecularity of an elementary reaction is determined by:

(A) Experiment only

(B) Temperature

(C) Energy released

(D) Stoichiometry of a single step

19. The technique used to analyze functional groups is:

(A) XRD

(B) IR spectroscopy

(C) Flame photometry

(D) UV spectroscopy

20. A unimolecular reaction usually follows:

(A) Second-order kinetics

(B) Zero-order kinetics

(C) First-order kinetics

(D) Third-order kinetics

21. NMR spectroscopy is based on:

(A) Vibrational energy

(B) Nuclear spin transitions

(C) Rotational energy

(D) Electron transitions

22. Molecularity cannot be determined from the:

(A) Elementary step

(B) Reaction mechanism

(C) Collision of molecules

(D) Balanced equation

23. Fingerprint region is found in:

(A) IR spectroscopy

(B) NMR

(C) UV spectroscopy

(D) Raman spectroscopy

24. The molecularity of decomposition of N₂O₅ in one step is:
(Single molecule decomposes)

(A) 3

(B) 2

(C) 1

(D) Cannot be determined

25. UV spectroscopy mainly involves transitions from:

(A) σ → σ* or π → π*

(B) Vibrational to rotational

(C) n → ground state

(D) Ionic to covalent

26. Molecularity depends on:

(A) Pressure

(B) Temperature

(C) Number of reacting particles

(D) Catalyst concentration

27. Raman shift is measured in units of:

(A) Newton

(B) cm⁻¹

(C) Coulomb

(D) Joule

28. A reaction having molecularity 2 is:

(A) Bimolecular

(B) Unimolecular

(C) Trimolecular

(D) Complex

29. In NMR, chemical shift is measured in:

(A) PPM

(B) Hz only

(C) Joules

(D) Kelvin

30. Molecularity is always a:

(A) Constant integer

(B) Fraction

(C) Variable

(D) Large number

31. Microwave spectroscopy studies:

(A) Electronic transitions

(B) Rotational transitions

(C) Nuclear transitions

(D) Lattice vibrations

32. A reaction cannot have molecularity more than:
(Probability becomes extremely low)

(A) Three

(B) Two

(C) One

(D) Four

33. UV-Vis absorption increases with:

(A) Light scattering

(B) Decrease in path length

(C) Increase in concentration

(D) Heat loss

34. Which is true for molecularity?

(A) Depends on pressure

(B) Can be predicted theoretically

(C) Always whole number

(D) Is always fractional

35. NMR detects:

(A) Ionic bonds

(B) Electron orbitals

(C) Proton environments

(D) Bond order only

36. A bimolecular reaction involves collision of:

(A) One molecule

(B) Many molecules

(C) Three molecules

(D) Two molecules

37. IR region is divided into:

(A) Low and high gamma

(B) Red and blue IR

(C) Near, mid, and far IR

(D) Light and dark IR

38. For molecularity, the slowest step is:

(A) Not important

(B) Unmeasurable

(C) Fast

(D) Rate-determining

39. UV transitions occur due to:

(A) Nuclear spin flips

(B) Electronic excitation

(C) Vibrational movements

(D) Bond stretching

40. Molecularity is not applicable to:

(A) Elementary steps

(B) Overall reactions

(C) Termolecular reactions

(D) Unimolecular reactions

41. IR radiation causes molecules to:

(A) Vibrate

(B) Ionize

(C) Decompose

(D) Radiate light

42. A reaction involving O₃ → O₂ + O has molecularity:

(A) 3

(B) 2

(C) 1

(D) 0

43. Raman spectroscopy detects:

(A) Mass of atoms

(B) Polarizability changes

(C) Electron spin

(D) Molecular mass

44. Molecularity and order are equal only when reaction is:

(A) Complex

(B) Elementary

(C) Reversible

(D) Catalyzed

45. NMR spectra splitting is caused by:

(A) Electron transitions

(B) Magnetic interactions between protons

(C) Dehydration

(D) Vibration of molecules

46. A reaction cannot have molecularity of:

(A) 4

(B) 2

(C) 3

(D) 1

47. IR absorption bands depend on:

(A) Electron transitions

(B) Proton spin

(C) Bond vibrations

(D) Solubility

48. In a bimolecular step, rate depends on:

(A) Only one reactant

(B) One intermediate

(C) No collisions

(D) Collision of two species

49. UV spectroscopy is useful for compounds with:

(A) Conjugated double bonds

(B) Isotopes

(C) Ionic bonds

(D) Covalent solids

50. Termolecular reactions have:

(A) Very high probability

(B) No collisions

(C) Low probability

(D) Always first-order kinetics