Assertion and Reason Questions for Class 11 Chemistry Chapter 4 Chemical Bonding and Molecular Structure

Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Q.1. Assertion : The bond order of helium is always zero.
Reason : The number of electrons in bonding molecular orbital and antibonding molecular orbital is equal.

Answer

Answer: (a)

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Q.2. Assertion : The lesser the lattice enthalpy more stable is the ionic compound.
Reason : The lattice enthalpy is greater, for ions of highest charge and smaller radii.

Answer

Answer: (d) Assertion is false but reason is true.
The greater the lattice enthalpy, more stable is the ionic compound.

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Q.3. Assertion : Atoms can combine either by transfer of valence of electrons from one atom to another or by sharing of valence electrons.
Reason : Sharing and transfer of valence electrons is done by atoms to have an octet in their valence shell.

Answer

Answer: (a) Atoms combine either by transfer of valence electrons from one atom to another or by sharing of valence electrons to have an octet in their valence shell.

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Q.4. Assertion : BF₃ molecule has zero dipole moment.
Reason : F is electronegative and B–F bonds are polar in nature.

Answer

Answer: (b)

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Q.5. Assertion : CH₂Cl₂ is non-polar and CCl₄ is polar molecule.
Reason : Molecule with zero dipole moment is non-polar in nature.

Answer

Answer: (d)

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Q.6. Assertion : Lone pair-lone pair repulsive interactions are greater than lone pair-bond pair and bond pair-bond pair interactions.
Reason : The space occupied by lone pair electrons is more as compared to bond pair electrons.

Answer

Answer: (a) While the lone pairs are localised on the central atom, each bonded pair is shared between two atoms. As a result, the lone pair electrons in a molecule occupy more space as compared to the bonding pairs of electrons. This results in greater repulsion between lone pairs of electrons as compared to the lone pair -bond pair and bond pair – bond pair repulsions.

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Q.7. Assertion : Sulphur compounds like SF₆ and H₂SO₄ have 12 valence electrons around S atom.
Reason : All sulphur compounds do not follow octet rule.

Answer

Answer: (c) Sulphur forms many compounds in which the octet rule is obeyed. For example SCl2 has an octet of electrons around it.

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Q.8. Assertion : In NH₃, N is sp³ hybridised, but angle is found to be 107°.
Reason : The decrease in bond angle is due to repulsion between the lone pair.

Answer

Answer: (a)

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Q.9. Assertion : pi bonds are weaker than σ bonds.
Reason : pi bonds are formed by the overlapping of p-p orbitals along their axes.

Answer

Answer: (a) Both assertion and reason are true and reason is the correct explanation of assertion.
pi bonds are formed by the overlapping of p-p orbitals perpendicular to their axis i.e., sidewise overlap.

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Q.10. Assertion : Water is one of the best solvent.
Reason : H-bonding is present in water molecules.

Answer

Answer: (b) Both assertion and reason are true but reason is not the correct explanation of assertion.
Water is excellent solvent because it has high value of dielectric constant. Due to high value of dielectric constant, the electrostatic force of attraction between the ions decrease and these ions get separated and ultimately get solvated by the solvent molecules.

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Q.11. Assertion : Bonding molecular orbital has greater stability than corresponding antibonding molecular orbital.
Reason : The electron density in a bonding molecular orbital is located away from the space between the nuclei while in antibonding molecular orbital it is located between the nuclei of the bonded atoms.

Answer

Answer: (c) The electron density in a bonding molecular orbital is located between the nuclei of the bonded atoms because of which the repulsion between the nuclei is very less while in case of an antibonding molecular orbital, most of the electron density is located away from the space between the nuclei. Electrons placed in a bonding molecular orbital tend to hold the nuclei together and stabilize a molecule.

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Q.12. Assertion : Shape of NH₃ molecule is tetrahedral.
Reason : In NH₃ nitrogen is sp³ hybridized.

Answer

Answer: (d) Assertion is false but reason is true.
NH3 molecule is pyramidal is shape, because out of four electron pairs, three are bonding pairs and one is lone pair.

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