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Metallic bonding and hydrogen bonding: NEET MCQs with answers

90 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. Which of the following organic compounds exhibits the highest solubility in water owing to effective intermolecular hydrogen bonding with water molecules?

  1. Triethylamine
  2. Acetonitrile
  3. Glucose
  4. Benzophenone
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Answer: (C) Glucose

Glucose (C₆H₁₂O₆) contains five hydroxyl (-OH) groups per molecule, enabling extensive and strong intermolecular hydrogen bonding with water molecules. This polyhydroxy structure confers extraordinarily high water solubility compared to simple amines, nitriles, or aromatic ketones.

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2. Given below are two statements: Assertion (A): o-Hydroxybenzaldehyde (salicylaldehyde) is steam-volatile, whereas p-hydroxybenzaldehyde is not. Reason (R): o-Hydroxybenzaldehyde exhibits intramolecular hydrogen bonding, which prevents intermolecular association and lowers its boiling point. In light of the above statements, choose the correct answer:

  1. Both (A) and (R) are true and (R) is the correct explanation of (A)
  2. Both (A) and (R) are true but (R) is NOT the correct explanation of (A)
  3. (A) is true but (R) is false
  4. (A) is false but (R) is true
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Answer: (A) Both (A) and (R) are true and (R) is the correct explanation of (A)

In o-hydroxybenzaldehyde, chelation via intramolecular hydrogen bonding between the -CHO and adjacent -OH group minimizes intermolecular attraction, leading to lower boiling point and steam volatility. In contrast, the p-isomer forms intermolecular hydrogen bonds, causing extensive molecular association and preventing steam distillation.

hard

3. In a hypothetical sample, 3.0 × 10²³ molecules of liquid water are present. Assuming every water molecule on average engages in 3.6 hydrogen bonds at this temperature, how many moles of hydrogen bonds exist in this sample? (Take N_A = 6.0 × 10²³ mol⁻¹)

  1. 0.90 mol
  2. 1.80 mol
  3. 3.60 mol
  4. 0.45 mol
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Answer: (A) 0.90 mol

Number of water molecules = 3.0 × 10²³ = 0.50 mol. Each hydrogen bond is shared between two molecules, meaning each molecule contributes 0.5 of an H-bond per interaction. Total moles of H-bonds = (moles of molecules × average bonds per molecule) / 2 = (0.50 × 3.6) / 2 = 1.80 / 2 = 0.90 mol.

medium

4. Which among the following metals is expected to have the highest enthalpy of atomization?

  1. Vanadium (V)
  2. Zinc (Zn)
  3. Scandium (Sc)
  4. Copper (Cu)
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Answer: (A) Vanadium (V)

The strength of metallic bonding and hence the enthalpy of atomization in transition metals depends directly on the number of unpaired d-electrons available for delocalization. Vanadium has 5 valence electrons (3d³ 4s²), all of which can participate in metallic bonding, giving it a higher enthalpy of atomization than Sc, Cu, or Zn (which has completely paired 3d¹⁰ electrons).

easy

5. Which of the following alkali metals is the softest and has the lowest melting point?

  1. Lithium (Li)
  2. Caesium (Cs)
  3. Rubidium (Rb)
  4. Sodium (Na)
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Answer: (B) Caesium (Cs)

As atomic size increases down the alkali metal group (Li to Cs), the distance between the metal nuclei and delocalized electron cloud increases. This weakens the metallic lattice, giving Caesium the lowest cohesive energy and lowest melting point (28.5 °C).

hard

6. Chloral hydrate, CCl₃CH(OH)₂, is an unusual gem-diol that is exceptionally stable and isolated as a crystalline solid at room temperature. What is the fundamental reason for its stability?

  1. Steric repulsion among the three chlorine atoms stabilizes the two -OH groups
  2. Resonance stabilization involving chlorine lone pairs donating into carbon 2p orbitals
  3. Intramolecular hydrogen bonding between chlorine atoms and the hydroxyl hydrogen atoms
  4. Extensive intermolecular metallic-like electron delocalization
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Answer: (C) Intramolecular hydrogen bonding between chlorine atoms and the hydroxyl hydrogen atoms

Gem-diols are generally thermodynamically unstable with respect to loss of water to form carbonyls. However, chloral hydrate is remarkably stable because each of the two -OH hydrogens forms a stable five-membered chelate ring via intramolecular hydrogen bonding with adjacent chlorine atoms (Cl···H-O).

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7. Which of the following statements is INCORRECT regarding hydrogen bonding?

  1. Intramolecular hydrogen bonding decreases the boiling point of a compound.
  2. Intermolecular hydrogen bonding increases the viscosity of a liquid.
  3. Hydrogen bonds are generally stronger than covalent single bonds.
  4. KHF₂ exists as a solid containing the symmetrical [F-H-F]⁻ ion.
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Answer: (C) Hydrogen bonds are generally stronger than covalent single bonds.

Hydrogen bonds are weak electrostatic attractions with bond energies typically between 10 to 40 kJ/mol, whereas covalent single bonds are much stronger, usually in the range of 150 to 450 kJ/mol.

hard

8. Given below are two statements: Statement I: Maleic acid (cis-butenedioic acid) has a much higher first dissociation constant (Ka₁) than fumaric acid (trans-butenedioic acid). Statement II: The monoanion of maleic acid is stabilized by intramolecular hydrogen bonding. In the light of the above statements, choose the correct answer:

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

In maleic acid, the two carboxyl groups are in cis configuration. Loss of one proton gives the hydrogen maleate monoanion, which forms a very stable 7-membered ring via intramolecular hydrogen bonding, strongly facilitating the first ionization (Ka₁ of maleic > fumaric).

easy

9. Which of the following hydrides shows the minimum boiling point among the group 15 hydrides?

  1. PH₃
  2. NH₃
  3. AsH₃
  4. SbH₃
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Answer: (A) PH₃

The boiling points of group 15 hydrides follow the order: BiH₃ > SbH₃ > NH₃ > AsH₃ > PH₃. PH₃ lacks significant hydrogen bonding due to low electronegativity and has the smallest molecular size and van der Waals forces compared to AsH₃ and SbH₃, making its boiling point the lowest in the group.

medium

10. The density of water shows an anomalous behavior where it reaches a maximum at 4 °C. This phenomenon occurs because:

  1. Covalent O-H bonds contract continuously up to 4 °C
  2. Hydrogen bonds completely vanish above 0 °C
  3. Breaking of the open-cage hydrogen-bonded structure predominates over thermal expansion up to 4 °C
  4. Water molecules polymerize into linear chains at 4 °C
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Answer: (C) Breaking of the open-cage hydrogen-bonded structure predominates over thermal expansion up to 4 °C

Between 0 °C and 4 °C, the collapse of the open, hollow cage-like hydrogen-bonded network of ice packs molecules closer together, increasing density faster than normal thermal expansion decreases it.

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11. Consider the following physical properties of metals: (I) Malleability (II) Ductility (III) Directional nature of bonding (IV) High electrical conductivity Which of these are directly consistent with the electron-sea model of metallic bonding?

  1. (I), (II) and (IV) only
  2. (I), (II) and (III) only
  3. (III) and (IV) only
  4. (I) and (IV) only
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Answer: (A) (I), (II) and (IV) only

Metallic bonds are completely non-directional because valence electrons are delocalized uniformly throughout the crystal lattice. When a stress is applied, atomic planes can slip over each other without breaking directional bonds, giving rise to malleability and ductility, while delocalized mobile electrons provide electrical conductivity.

easy

12. The correct increasing order of metallic bond strength among the alkali metals is:

  1. Na < K < Rb < Cs < Li
  2. Li < Na < K < Rb < Cs
  3. Cs < Rb < K < Na < Li
  4. Cs < Li < Na < K < Rb
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Answer: (C) Cs < Rb < K < Na < Li

Metallic bond strength depends inversely on atomic size and directly on effective nuclear attraction toward the delocalized valence electron cloud. As the atomic radius increases down Group 1 from Li to Cs, the electrostatic attraction between the metal cations and the delocalized electron sea weakens, so metallic bond strength decreases: Cs < Rb < K < Na < Li.

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