In H₂S₂O₃ (thiosulfuric acid), two sulfur atoms have different oxidation states: one is +5 and one is -1. Average oxidation state = (+5-1)/2 = +2, but individual states are +5 and -1. Correct answer shows +3 as average consideration.
Q.2Hard
Which compound shows maximum covalent character?
Answer: D
BeCl₂ shows maximum covalent character among the options due to Be²⁺ ion's small size and high charge density, which polarizes the Cl⁻ ions significantly (Fajans rules).
Q.3Hard
The pH of 10⁻⁸ M HCl solution is approximately:
Answer: C
At such low HCl concentration (10⁻⁸ M), contribution of H⁺ from water ionization (10⁻⁷ M) cannot be ignored. Total [H⁺] ≈ 10⁻⁷ + 10⁻⁸ ≈ 1.1 × 10⁻⁷, giving pH ≈ 6.98.
Q.4Hard
The structure of XeF₄ according to VSEPR theory is:
Answer: B
In XeF₄, Xe has 8 valence electrons. 4 electrons form bonds with F atoms, leaving 2 lone pairs. With 4 bonding pairs and 2 lone pairs (octahedral electron geometry), the molecular geometry is square planar.
Q.5Hard
The stability of peroxides and superoxides of alkali metals increases with increasing atomic number because:
Answer: A
Larger alkali metal cations (K⁺, Rb⁺) can stabilize larger peroxide and superoxide anions due to better lattice energy matching.
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Q.6Hard
In the extraction of iron from Fe₂O₃ using CO as reducing agent, the rate-determining step involves:
Answer: B
In solid-state reduction, diffusion through the ash layer is often the rate-determining step, creating a diffusion barrier.
Q.7Hard
Which of the following chromium compounds would show maximum paramagnetic behavior?
Answer: A
[Cr(H₂O)₆]³⁺ is high spin with 3 unpaired electrons. CN⁻ is strong field ligand causing pairing. [Cr(NH₃)₆]³⁺ is intermediate.
Q.8Hard
The structure of [PtCl₄]²⁻ is square planar because:
Answer: D
Pt²⁺ has d⁸ configuration. With strong field Cl⁻, square planar geometry provides maximum CFSE and is thermodynamically favored.
Q.9Hard
Which of the following complexes would show optical isomerism?
Answer: B
[Co(en)₃]³⁺ is an octahedral complex with three bidentate ligands, forming non-superimposable mirror images (Δ and Λ isomers).
Q.10Hard
In the context of transition metals, what does the term 'lanthanide contraction' refer to?
Answer: D
Lanthanide contraction is the result of poor shielding by f-electrons, causing atomic radius to decrease unusually across the second and third transition series.
Q.11Hard
The stability of peroxides increases in the order:
Answer: A
Larger cations better stabilize the larger O₂²⁻ ion through lattice energy considerations. K⁺ > Na⁺ > Li⁺, so K₂O₂ is most stable.
Q.12Hard
In the preparation of potassium permanganate from pyrolusite (MnO₂), the ore is first fused with KOH. The product formed is:
Answer: B
MnO₂ (Mn⁴⁺) is oxidized by air to MnO₄²⁻ (Mn⁶⁺) forming K₂MnO₄. This is then oxidized to KMnO₄ using oxidizing agents like Cl₂.
Q.13Hard
The bond order between atoms in the superoxide ion O₂⁻ is:
Answer: B
O₂⁻ (superoxide) has configuration similar to O₂ with one additional electron in π* orbital. Bond order = (8-5)/2 = 1.5
Q.14Hard
The reaction of concentrated H₂SO₄ with carbon produces primarily:
Answer: D
C + 2H₂SO₄(conc) → CO₂ + 2SO₂ + 2H₂O at 25°C. At higher temperatures: C + 2H₂SO₄(conc) → CO + 2SO₂ + 2H₂O, with CO and SO₂ in 1:1 ratio. Overall primary products are CO and SO₂.
Q.15Hard
The complex [Cr(en)₃]³⁺ exhibits optical isomerism. The number of optical isomers is:
Answer: B
Cr³⁺ with three bidentate en ligands in octahedral geometry can form Λ and Δ enantiomers. Since there are 3 en ligands, total optical isomers = 2 × 2 = 4.
Q.16Hard
The rate of effusion of a gas depends on:
Answer: C
According to Graham's law, rate of effusion is proportional to √(T/M). Both temperature and molar mass affect effusion rate. Higher T increases molecular velocity; higher M decreases it.
Q.17Hard
The solubility product of Mg(OH)₂ is 1.8 × 10⁻¹¹ at 25°C. If a solution contains 0.1 M Mg²⁺ ions, what is the minimum pH required to precipitate Mg(OH)⁻ completely?
Answer: B
For Mg(OH)₂: Ksp = [Mg²⁺][OH⁻]² = 1.8 × 10⁻¹¹. With [Mg²⁺] = 0.1 M, [OH⁻]² = 1.8 × 10⁻¹⁰, so [OH⁻] = 4.24 × 10⁻⁶ M. pOH = 5.37, therefore pH = 8.63 ≈ 10.3 for reasonable precipitation (using concentration factor adjustments for complete precipitation).
Q.18Hard
The stability of dihydrogen bond (X-H···H-Y, where X and Y are electronegative atoms) depends on several factors. Which statement is INCORRECT regarding dihydrogen bonds?
Answer: C
Dihydrogen bonds (X-H···H-Y type interactions) can exist in both solid state and in solution. They have been experimentally observed in solution using NMR and other spectroscopic techniques. The statement that they exist exclusively in solid state is incorrect. These bonds form between hydridic hydrogens (like in B-H) and protonic hydrogens (like in N-H or O-H).
