Q21. Lead (IV) compounds are less stable than lead (II) compounds due to:
A) Greater metallic character of lead.
B) Higher electronegativity of lead.
C) Inert pair effect.
D) Smaller atomic size of lead.
Answer: C) Inert pair effect
Explanation: The inert pair effect causes the s-electrons to remain paired and not participate in bonding, making the +2 oxidation state more stable for lead than the +4 oxidation state.
Q22. Which of the following elements of Group 14 forms both ionic and covalent halides?
A) Carbon
B) Silicon
C) Germanium
D) Lead
Answer: D) Lead
Explanation: Lead forms covalent compounds like PbCl₄ in the +4 oxidation state and ionic compounds like PbCl₂ in the +2 oxidation state, reflecting the stability of the +2 state due to the inert pair effect.
Q23. The strongest allotrope of carbon is:
A) Graphite
B) Diamond
C) Fullerene
D) Carbon nanotubes
Answer: B) Diamond
Explanation: Diamond is the hardest known natural material because of its tetrahedral structure, where each carbon atom is strongly covalently bonded to four other carbon atoms.
Q24. Silica (SiO₂) has a structure similar to:
A) Diamond
B) Graphite
C) Fullerene
D) NaCl
Answer: A) Diamond
Explanation: Silica (SiO₂) has a network covalent structure similar to diamond, where each silicon atom is bonded to four oxygen atoms in a tetrahedral arrangement, leading to a rigid 3D structure.
Nitrogen Family
Q25. Nitrogen exists as a diatomic molecule, whereas phosphorus exists as:
A) Diatomic molecules
B) P₄ molecules
C) P₃ molecules
D) P₂ molecules
Answer: B) P₄ molecules
Explanation: Nitrogen forms stable diatomic molecules (N₂) with a triple bond. Phosphorus, on the other hand, exists as P₄ tetrahedral molecules due to its inability to form strong triple bonds like nitrogen.
Q26. The anomalous behavior of nitrogen among Group 15 elements is due to:
A) Absence of d-orbitals
B) High electronegativity
C) Small atomic size
D) All of the above
Answer: D) All of the above
Explanation: Nitrogen differs from other Group 15 elements because it has no d-orbitals, high electronegativity, and small atomic size. These factors lead to its unique properties like the formation of N₂ with a triple bond.
Q27. Ammonia (NH₃) has a higher boiling point than phosphine (PH₃) because:
A) Ammonia is heavier.
B) Ammonia forms hydrogen bonds.
C) Ammonia has a larger molecular size.
D) Ammonia is a polar molecule.
Answer: B) Ammonia forms hydrogen bonds.
Explanation: Ammonia molecules form strong intermolecular hydrogen bonds due to the high electronegativity of nitrogen, leading to a higher boiling point compared to phosphine, which does not form hydrogen bonds as effectively.
Q28. Nitric acid (HNO₃) acts as a strong acid because:
A) It dissociates completely in water.
B) It is a weak electrolyte.
C) It forms covalent bonds in water.
D) It is amphoteric.
Answer: A) It dissociates completely in water.
Explanation: Nitric acid (HNO₃) is a strong acid that dissociates completely in water to produce H⁺ and NO₃⁻ ions, making it highly acidic.
Q29. Phosphorus pentachloride (PCl₅) in solid state exists as:
A) PCl₅ molecules
B) PCl₄⁺ and PCl₆⁻ ions
C) P₂Cl₁₀ molecules
D) P₄ molecules
Answer: B) PCl₄⁺ and PCl₆⁻ ions
Explanation: In the solid state, PCl₅ exists in the ionic form as PCl₄⁺ and PCl₆⁻ ions, which stabilize the solid structure. In the gaseous state, PCl₅ exists as discrete molecules.
Q30. The most stable oxidation state of bismuth (Bi) is:
A) +1
B) +3
C) +5
D) -3
Answer: B) +3
Explanation: Due to the inert pair effect, the +3 oxidation state is the most stable for bismuth, with the +5 oxidation state being less stable as we go down the group.
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