TRB PG Assistant - Molecular orbital theory for diatomic and simple triatomic molecules Online Test (MCQ Quiz)

1. According to Molecular Orbital Theory (MOT), what is the fundamental difference between atomic orbitals and molecular orbitals?

A) Atomic orbitals are formed by the overlap of atomic nuclei, while molecular orbitals are formed by the overlap of electron clouds. B) Atomic orbitals are associated with individual atoms, while molecular orbitals are delocalized over the entire molecule. C) Atomic orbitals have fixed energy levels, while molecular orbitals have variable energy levels. D) Atomic orbitals are spherical, while molecular orbitals are always dumbbell-shaped.

2. When two atomic orbitals combine to form molecular orbitals, how many molecular orbitals are formed?

A) One B) Two C) Three D) The number depends on the type of atomic orbitals.

3. What type of molecular orbitals are formed when atomic orbitals combine in-phase (constructive interference)?

A) Antibonding molecular orbitals B) Non-bonding molecular orbitals C) Bonding molecular orbitals D) Hybrid molecular orbitals

4. What is the characteristic feature of an antibonding molecular orbital compared to a bonding molecular orbital?

A) Lower energy and increased electron density between nuclei B) Higher energy and decreased electron density between nuclei C) Equal energy and uniform electron density throughout the molecule D) Lower energy and uniform electron density throughout the molecule

5. Which symbol is used to denote an antibonding molecular orbital formed from s orbitals?

A) σ B) π C) σ* D) π*

6. What is the primary condition for the linear combination of atomic orbitals (LCAO) to form molecular orbitals?

A) Atomic orbitals must have different energies. B) Atomic orbitals must have the same symmetry and comparable energies. C) Atomic orbitals must be orthogonal to each other. D) Atomic orbitals must be filled with electrons.

7. In the MOT diagram of H₂, how many electrons are present in the bonding σ molecular orbital?

A) 0 B) 1 C) 2 D) 4

8. What is the bond order of H₂ according to MOT?

A) 0 B) 0.5 C) 1 D) 2

9. What does a bond order of 1 indicate for a diatomic molecule?

A) No bond exists between the atoms. B) A single covalent bond exists between the atoms. C) A double covalent bond exists between the atoms. D) The molecule is unstable.

10. Which diatomic molecule is predicted to be paramagnetic by MOT but is observed to be diamagnetic?

A) H₂ B) He₂ C) Li₂ D) O₂

11. In the MOT diagram of He₂, how many electrons occupy the antibonding σ* molecular orbital?

A) 0 B) 1 C) 2 D) 4

12. What is the calculated bond order for He₂ using MOT?

A) 0 B) 0.5 C) 1 D) 2

13. The molecular orbital configuration of Li₂ is (σ₂s)² (σ*₂s)² (σ₂p)².

A) True B) False C) Partially true D) Cannot be determined

14. What is the bond order of Li₂?

A) 0 B) 1 C) 1.5 D) 2

15. Which of the following diatomic molecules has the highest bond order?

A) Li₂ B) Be₂ C) B₂ D) C₂

16. In the MOT diagram for homonuclear diatomic molecules of the second period (Li₂ to N₂), which molecular orbitals are formed by the sideways overlap of p-orbitals?

A) σ₂p and σ*₂p B) π₂p and π*₂p C) σ₂s and σ*₂s D) Only π bonding orbitals

17. For diatomic molecules from O₂ to Ne₂, the energy order of molecular orbitals is different from Li₂ to N₂. Which statement correctly describes this difference?

A) The σ₂p orbital is lower in energy than the π₂p orbitals. B) The π₂p orbitals are lower in energy than the σ₂p orbital. C) The σ*₂p orbital is lower in energy than the π*₂p orbitals. D) The π*₂p orbitals are lower in energy than the σ*₂p orbital.

18. What is the number of unpaired electrons in O₂ according to MOT?

A) 0 B) 1 C) 2 D) 3

19. What is the bond order of O₂?

A) 1 B) 1.5 C) 2 D) 2.5

20. Which of the following diatomic molecules is diamagnetic?

A) B₂ B) C₂ C) N₂ D) O₂

21. What is the bond order of N₂?

A) 1 B) 2 C) 2.5 D) 3

22. The molecule F₂ has the molecular orbital configuration (σ₂s)² (σ*₂s)² (σ₂p)² (π₂p)⁴ (π*₂p)⁴. What is its bond order?

A) 0 B) 1 C) 1.5 D) 2

23. Which diatomic molecule is expected to be the most stable based on bond order?

A) N₂ B) O₂ C) F₂ D) Ne₂

24. When are π molecular orbitals formed in diatomic molecules?

A) By the end-on overlap of s orbitals. B) By the end-on overlap of p orbitals. C) By the sideways overlap of p orbitals. D) By the overlap of d orbitals.

25. What is the primary advantage of using MOT over Valence Bond Theory (VBT) for explaining the properties of molecules?

A) VBT can explain paramagnetism of O₂. B) MOT can explain paramagnetism and diamagnetism of molecules. C) VBT is simpler to apply. D) VBT accurately predicts bond lengths.

26. In the context of MOT, what is the significance of the number of electrons in antibonding molecular orbitals?

A) They increase bond strength. B) They decrease bond strength. C) They have no effect on bond strength. D) They are responsible for paramagnetism.

27. Which of the following is NOT a type of molecular orbital formed from the combination of atomic orbitals?

A) Bonding molecular orbital B) Antibonding molecular orbital C) Non-bonding molecular orbital D) Hybrid molecular orbital

28. Consider the diatomic molecule CO. Which atomic orbitals are primarily involved in forming the σ molecular orbitals?

A) 2s and 2p orbitals of Carbon and Oxygen B) Only 2s orbitals of Carbon and Oxygen C) Only 2p orbitals of Carbon and Oxygen D) Hybrid orbitals of Carbon and Oxygen

29. The molecular orbital diagram for heteronuclear diatomic molecules like CO is similar to homonuclear ones, but with a key difference in orbital energies. What is this difference?

A) The atomic orbitals of the more electronegative atom are lower in energy. B) The atomic orbitals of the less electronegative atom are lower in energy. C) The molecular orbitals are always degenerate. D) The bond order is always fractional.

30. What is the bond order of CO based on its molecular orbital configuration?

A) 1 B) 2 C) 2.5 D) 3

31. Which statement best describes the bonding in NO according to MOT?

A) It is diamagnetic with a bond order of 2. B) It is paramagnetic with a bond order of 2.5. C) It is diamagnetic with a bond order of 2.5. D) It is paramagnetic with a bond order of 2.

32. In the molecular orbital diagram of Be₂, the electrons fill up to which set of molecular orbitals?

A) (σ₂s)² (σ*₂s)² B) (σ₂s)² (σ*₂s)² (σ₂p)² C) (σ₂s)² (σ*₂s)² (π₂p)² D) (σ₂s)² (σ*₂s)² (π₂p)² (π*₂p)²

33. The bond order of B₂ is 1. What is the correct molecular orbital configuration for B₂?

A) (σ₂s)² (σ*₂s)² (σ₂p)² (π₂p)² B) (σ₂s)² (σ*₂s)² (π₂p)² C) (σ₂s)² (σ*₂s)² (σ₂p)² D) (σ₂s)² (σ*₂s)² (π₂p)² (π*₂p)²

34. Which of the following diatomic ions has a bond order of 3?

A) O₂²⁻ B) N₂⁻ C) C₂²⁻ D) Li₂⁺

35. What is the bond order of the O₂⁻ ion?

A) 1 B) 1.5 C) 2 D) 2.5

36. According to MOT, diatomic molecules with a bond order of zero are:

A) Stable and exist B) Unstable and do not exist C) Paramagnetic D) Diatomic in nature but with no covalent bond

37. The HOMO (Highest Occupied Molecular Orbital) of N₂ is:

A) σ₂p B) π₂p C) σ*₂p D) π*₂p

38. The LUMO (Lowest Unoccupied Molecular Orbital) of O₂ is:

A) σ₂p B) π₂p C) σ*₂p D) π*₂p

39. In the formation of π bonding molecular orbitals from p-orbitals, the electron density is concentrated:

A) Along the internuclear axis. B) Above and below the internuclear axis. C) Within the atomic nuclei. D) Equally in all directions.

40. Which of the following best describes the molecular orbitals formed from the combination of two 2p atomic orbitals oriented end-to-end?

A) One σ bonding and one π antibonding orbital B) One π bonding and one σ antibonding orbital C) One σ bonding and one σ antibonding orbital D) Two π bonding and two π antibonding orbitals

41. The energy difference between bonding and antibonding molecular orbitals is generally:

A) Smaller than the energy difference between the original atomic orbitals. B) Larger than the energy difference between the original atomic orbitals. C) Equal to the energy difference between the original atomic orbitals. D) Dependent on the molecule's polarity.

42. For a molecule like CO, which atom's atomic orbitals contribute more significantly to the lower energy molecular orbitals?

A) Carbon (less electronegative) B) Oxygen (more electronegative) C) Both contribute equally D) It depends on the bond order.

43. Which of the following species would be expected to be paramagnetic?

A) N₂ B) CN⁻ C) O₂⁻ D) F₂

44. What is the bond order of the diatomic molecule B₂?

A) 0 B) 0.5 C) 1 D) 1.5

45. The spectral transition responsible for the color of a substance is related to the energy difference between:

A) Adjacent atomic orbitals. B) Bonding and antibonding molecular orbitals. C) Non-bonding and antibonding molecular orbitals. D) The HOMO and LUMO.

46. In the molecular orbital diagram of O₂, the π*₂p orbitals are filled with how many electrons?

A) 2 B) 3 C) 4 D) 6

47. Which of the following correctly orders the bond strength of diatomic molecules according to MOT?

A) N₂ > O₂ > F₂ B) O₂ > N₂ > F₂ C) F₂ > O₂ > N₂ D) N₂ > F₂ > O₂

48. What is the primary reason for the existence of homonuclear diatomic molecules of elements from Li to N showing s-p mixing?

A) Stronger overlap between 2s and 2p orbitals. B) Close energy proximity of 2s and 2p atomic orbitals. C) Repulsion between electrons in 2p orbitals. D) The symmetry of the molecule.

49. The molecule O₂⁺ has one less electron than O₂. How does this affect its bond order and stability compared to O₂?

A) Lower bond order, less stable B) Higher bond order, more stable C) Same bond order, same stability D) Lower bond order, more stable

50. According to MOT, what is the electronic configuration of the ground state of B₂?

A) (σ₂s)² (σ*₂s)² (σ₂p)² B) (σ₂s)² (σ*₂s)² (π₂p)² C) (σ₂s)² (σ*₂s)² (π₂p)² (π*₂p)² D) (σ₂s)² (σ*₂s)² (σ₂p)² (π₂p)²

Molecular orbital theory for diatomic and simple triatomic molecules - Online Test

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