Which of the following statements about diborane (B₂H₆) is incorrect?
Answer: C
B₂H₆ has a bridged structure with 3D geometry, not planar. It contains bridging hydrogens forming 3-center-2-electron bonds.
Q.262Easy
The standard electrode potential for Zn²⁺/Zn is -0.76 V. In a galvanic cell combining Zn and Cu electrodes, Zn will act as:
Answer: B
Zn has lower (more negative) reduction potential than Cu, making it more easily oxidized. It acts as the anode (negative electrode) in the galvanic cell.
Q.263Hard
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.264Hard
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.265Easy
The primary use of zinc in brass alloy is to:
Answer: C
Zinc in brass (Cu-Zn alloy) enhances corrosion resistance through protective layer formation and improves cold-workability of copper.
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Q.266Medium
The complex [Ni(CN)₄]²⁻ is diamagnetic. This indicates:
Answer: B
Ni²⁺ with strong field CN⁻ ligands shows diamagnetism (d⁸ with all paired electrons) in square planar geometry (dsp² hybridization).
Q.267Hard
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.268Easy
Which of the following noble gases has the lowest ionization energy?
Answer: D
Ionization energy decreases down a group. Xenon (54 electrons) has the largest atomic radius and lowest ionization energy among noble gases listed.
Q.269Medium
In the preparation of chlorine by oxidizing HCl with MnO₂, the oxidation state of Mn changes from:
Answer: B
MnO₂ (Mn⁴⁺) acts as oxidizing agent, reducing Cl⁻ to Cl₂. Mn⁴⁺ gains 2 electrons, reducing to Mn²⁺.
Q.270Easy
The coordination number of Co in [Co(NH₃)₆]³⁺ complex is:
Answer: C
Coordination number is the number of ligands bonded to the central metal. Six NH₃ molecules surround Co³⁺, giving coordination number 6.
Q.271Medium
Which of the following factors does NOT affect the magnitude of crystal field splitting (Δ)?
Answer: C
Crystal field splitting depends on ligand strength, metal ion charge, and geometry, but NOT on the mass of the metal ion.
Q.272Hard
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.273Medium
Which of the following elements forms the most stable +6 oxidation state in its compounds?
Answer: C
Tungsten forms the most stable +6 oxidation state compounds like WO₃ and WCl₆. The stability of +6 state decreases from W to Mo to Cr due to increasing ease of reduction.
Q.274Easy
In the extraction of iron from haematite using blast furnace, the reducing agent is primarily:
Answer: A
CO produced in the blast furnace acts as the primary reducing agent for Fe₂O₃. Although coke is fed, CO generated from coke combustion performs the actual reduction.
Q.275Easy
The hybridization of sulphur in SF₆ molecule is:
Answer: C
SF₆ has 6 fluorine atoms bonded to sulphur with octahedral geometry. The hybridization is sp³d² involving d-orbitals from the third shell.
Q.276Medium
Which transition metal forms a complex with CO that has maximum carbonyl stretching frequency?
Answer: C
Manganese with lower electron density shows weaker back-bonding, resulting in higher CO stretching frequency. The order is Mn > Co > Fe > Ni based on back-bonding strength.
Q.277Easy
The aqueous solution of which salt is most acidic due to hydrolysis?
Answer: B
FeCl₃ undergoes significant hydrolysis: Fe³⁺ + H₂O ⇌ Fe(OH)²⁺ + H⁺. Fe³⁺ is a strong Lewis acid causing extensive hydrolysis and acidic solution.
Q.278Easy
In the contact process for H₂SO₄ manufacture, the catalyst used is:
Answer: B
V₂O₅ is the standard catalyst used in the oxidation of SO₂ to SO₃. It provides excellent activity and selectivity at 400-450°C operational temperature.
Q.279Medium
The magnetic moment of [Fe(H₂O)₆]²⁺ complex is approximately:
Answer: D
Fe²⁺ has d⁶ configuration. In octahedral geometry with weak field ligand H₂O, it remains high spin with 4 unpaired electrons giving μ = √[4(4+2)] ≈ 4.90 BM, but aqua complex shows ~5.92 BM.
Q.280Medium
Which of the following chlorides is most covalent in nature?
Answer: D
SiCl₄ is most covalent due to small Si⁴⁺ size and high charge density. Covalent character increases: NaCl < MgCl₂ < AlCl₃ < SiCl₄.
