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Valence-bond theory, hybridization and resonance: NEET MCQs with answers

57 questions on this topic of Chemical Bonding and Molecular Structure (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. Consider the following statements regarding Valence Bond Theory: Statement I: A covalent bond is formed by the overlapping of two half-filled valence atomic orbitals having electrons with opposite spins. Statement II: The strength of a covalent bond depends upon the extent of overlapping of the participating atomic orbitals. Choose the correct option:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
Show answer and explanation

Answer: (A) Both Statement I and Statement II are correct

According to valence bond theory, a covalent bond involves the pairing of electrons with antiparallel spins via overlapping half-filled orbitals. Greater extent of atomic orbital overlap leads to greater electron density between nuclei and a stronger covalent bond.

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2. In the molecule hydrazoic acid (HN₃), what are the hybridization states of the three nitrogen atoms designated as H-N(1)=N(2)≡N(3)?

  1. N(1) is sp², N(2) is sp, N(3) is sp
  2. N(1) is sp³, N(2) is sp², N(3) is sp
  3. N(1) is sp², N(2) is sp², N(3) is sp
  4. N(1) is sp, N(2) is sp, N(3) is sp
Show answer and explanation

Answer: (A) N(1) is sp², N(2) is sp, N(3) is sp

In the Lewis structure H-N=N⁺=N⁻ or H-N-N⁺≡N, N(1) has two σ-bonds (to H and N(2)) and one lone pair, giving a steric number of 3 (sp²). The central N(2) atom has two σ-bonds and no lone pairs, so it is sp-hybridized. The terminal N(3) atom participates in a triple bond with one lone pair or a double bond with two lone pairs, exhibiting sp-hybridization.

hard

3. The d-orbitals involved in the sp³d² hybridization of the central atom in an octahedral complex or molecule (such as SF₆) are:

  1. dxy and dyz
  2. dxz and dyz
  3. dz² and dx²-y²
  4. dxy and dx²-y²
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Answer: (C) dz² and dx²-y²

Octahedral geometry requires orbital lobes directed along the three Cartesian axes (x, y, and z). The two d-orbitals with lobes oriented along the coordinate axes are dz² and dx²-y², which participate in sp³d² (or d²sp³) hybridization.

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4. In the molecule vinylacetylene (CH₂=CH-C≡CH), the total number of σ (sigma) and π (pi) bonds respectively is:

  1. 7 and 3
  2. 6 and 3
  3. 7 and 2
  4. 8 and 2
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Answer: (A) 7 and 3

Vinylacetylene has the expanded structure H₂C=CH-C≡C-H. Counting single/sigma components: 3 C-H single bonds in vinyl part + 1 C=C (1 σ) + 1 C-C single bond + 1 C≡C (1 σ) + 1 C-H on alkyne = 7 σ-bonds. For π-bonds: 1 from C=C and 2 from C≡C = 3 π-bonds.

easy

5. Which of the following overlaps of atomic orbitals is non-bonding or zero overlap along the internuclear z-axis?

  1. s and pz orbital
  2. pz and pz orbital
  3. s and px orbital
  4. dxz and px orbital
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Answer: (C) s and px orbital

When an s orbital approaches a px orbital along the z-axis, the positive lobe of the s orbital overlaps equally with the positive and negative lobes of the px orbital. The net overlap is zero due to destructive cancellation, resulting in zero or non-bonding overlap.

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6. Which d-orbitals are involved in the hybridization of the central atom in chlorine pentafluoride (ClF₅)?

  1. d_xy and d_yz
  2. d_xz and d_yz
  3. d_z² and d_x²-y²
  4. d_z² and d_xy
Show answer and explanation

Answer: (C) d_z² and d_x²-y²

In ClF₅, chlorine has 5 bond pairs and 1 lone pair, requiring sp³d² hybridization with octahedral electron-pair geometry. The two d-orbitals that point directly along the Cartesian axes and participate in sp³d² hybridization are d_z² and d_x²-y².

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7. The hybridisation of the central atom in NH₃ is:

  1. sp³d²
  2. sp²
  3. sp³
  4. sp³d
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Answer: (C) sp³

Counting bond pairs and lone pairs on the central atom of NH₃ gives sp³ hybridisation.

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8. What is the state of hybridization of the central nitrogen atoms in the cation and anion of solid dinitrogen pentoxide [NO₂]⁺[NO₃]⁻?

  1. sp² and sp³
  2. sp and sp²
  3. sp and sp³
  4. sp² and sp
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Answer: (B) sp and sp²

Solid N₂O₅ exists as [NO₂]⁺[NO₃]⁻. In the linear nitronium cation ([NO₂]⁺), nitrogen has 2 bond pairs and 0 lone pairs, giving sp hybridization. In the planar nitrate anion ([NO₃]⁻), nitrogen has 3 bonding regions and 0 lone pairs, giving sp² hybridization.

easy

9. What are the hybridization states of the carbon atoms in methyl isocyanate (CH₃-N=C=O) from left to right?

  1. sp³ and sp
  2. sp³ and sp²
  3. sp² and sp
  4. sp³ and sp³
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Answer: (A) sp³ and sp

The methyl carbon is bonded to three hydrogen atoms and one nitrogen atom via four single σ-bonds, making it sp³-hybridized. The carbonyl carbon forms two σ-bonds (one with N and one with O) and two π-bonds, giving it a steric number of 2, which corresponds to sp-hybridization.

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10. Which specific d-orbital is involved in the hybridization of the central atom in phosphorus pentachloride (PCl₅) in the gaseous state?

  1. dz²
  2. dx²-y²
  3. dxy
  4. dxz
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Answer: (A) dz²

Phosphorus in gaseous PCl₅ exhibits trigonal bipyramidal geometry resulting from sp³d hybridization. The set of orbitals used in sp³d hybridization is s + px + py + pz + dz² because the lobes of the dz² orbital point along the axial z-axis.

easy

11. In the resonance hybrid of the carbonate ion (CO₃²⁻), the carbon-oxygen bond order is:

  1. 1.00
  2. 2.00
  3. 1.50
  4. 1.33
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Answer: (D) 1.33

Carbonate ion has three equivalent canonical structures where 4 pairs of bonding electrons are shared among 3 C-O bond positions. Therefore, the average bond order for each C-O bond is 4/3 = 1.33.

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12. The hybridisation of the central atom in H₂O is:

  1. sp³
  2. sp³d
  3. sp³d²
  4. sp²
Show answer and explanation

Answer: (A) sp³

Counting bond pairs and lone pairs on the central atom of H₂O gives sp³ hybridisation.

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