Chemistry carries the highest scoring potential in JEE for anyone who keeps the three branches separate in revision. This set covers physical chemistry numericals, organic reaction mechanisms and named reactions, and inorganic chemistry including periodic trends, chemical bonding and coordination compounds. Organic questions show the mechanism arrow by arrow, so the reasoning transfers to reactions you have not seen before.
The disproportionation of H₂O₂ in acidic medium is catalyzed by:
Answer: C
Both MnO₂ and Pt catalyze H₂O₂ decomposition to H₂O and O₂. MnO₂ is a heterogeneous catalyst while Pt can function as both heterogeneous and homogeneous catalyst.
Q.282Easy
The oxidation state of bromine in KBrO₄ is:
Answer: B
In KBrO₄, K is +1 and each O is -2. Therefore: 1 + x + 4(-2) = 0, giving x = +7. Bromine achieves its maximum oxidation state in this perbromate ion.
Q.283Easy
Which element shows variable oxidation states primarily due to incomplete d-orbitals?
Answer: C
Transition metals like Mn show multiple oxidation states (+2, +3, +4, +6, +7) due to incomplete d-orbitals. Zn shows only +2, Cu shows +1 and +2.
Q.284Medium
The geometry of [PtCl₄]²⁻ complex is:
Answer: B
Pt²⁺ is d⁸ with strong field Cl⁻ ligands. The dsp² hybridization gives square planar geometry, which is the preferred geometry for d⁸ complexes with strong field ligands.
Q.285Medium
The rate of precipitation of AgCl from a solution is fastest when:
Answer: D
Rapid mixing increases collision frequency. The presence of AgCl seed crystal provides nucleation sites. Both factors enhance precipitation rate by different mechanisms.
Q.286Medium
In aqueous solution, which ion hydrolyzes to the maximum extent?
Answer: B
Be²⁺ has the smallest size and highest charge density, making it the strongest Lewis acid. It undergoes extensive hydrolysis. The order is Be²⁺ > Al³⁺ > Mg²⁺ > Ba²⁺.
Q.287Medium
The bond angle in PCl₃ molecule is approximately:
Answer: B
PCl₃ has trigonal pyramidal geometry due to one lone pair on P. The bond angle is reduced from 120° (ideal trigonal) to 101.8° due to lone pair repulsion.
Q.288Medium
Which of the following compounds shows maximum lattice energy?
Answer: B
MgO has the highest lattice energy due to smallest cation (Mg²⁺) and anion (O²⁻) sizes combined with higher charges. Order: MgO > NaCl > CaO > KCl.
Q.289Medium
The ionization potential of beryllium is higher than boron because:
Answer: C
Be (1s² 2s²) has a filled 2s orbital which is more stable. Additionally, smaller size means electrons are closer to nucleus. Both factors increase ionization potential.
Q.290Easy
In the preparation of oxygen by thermal decomposition of KClO₃, the catalyst used is:
Answer: A
MnO₂ is the standard catalyst for KClO₃ decomposition, significantly lowering the decomposition temperature from ~400°C to ~240°C. It acts as a heterogeneous catalyst.
Q.291Hard
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.292Hard
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.293Medium
When a solution of potassium permanganate is diluted with water in the presence of ethanol, the purple color fades. This is because:
Answer: C
Permanganate ions (MnO₄⁻) oxidize ethanol to acetaldehyde and are themselves reduced to colorless Mn²⁺ ions (or MnO₂ depending on pH), causing the purple color to fade. This is a classic redox reaction where the oxidation state of Mn changes from +7 to +2.
Q.294Medium
Which of the following lanthanide elements has the electronic configuration [Xe]4f⁷5d¹6s²?
Answer: A
Gadolinium has atomic number 64 with configuration [Xe]4f⁷5d¹6s². The half-filled 4f⁷ configuration makes Gd exceptionally stable. This is the only lanthanide with a 5d electron, making it unique among the lanthanide series.
Q.295Hard
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.296Easy
In the extraction of iron from its ore using a blast furnace, the temperature at the bottom of the furnace reaches approximately 1900°C. At this temperature, which compound primarily acts as the reducing agent?
Answer: B
At high temperatures in the blast furnace, carbon monoxide (CO) is the primary reducing agent that converts iron oxides to metallic iron. Although coke produces CO, the actual reduction occurs through CO: Fe₂O₃ + 3CO → 2Fe + 3CO₂. This is thermodynamically favorable at furnace temperatures.
Q.297Hard
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).
Q.298Easy
Which of the following is the SI unit of electrical conductivity?
Answer: A
Electrical conductivity is measured in Siemens per meter (S·m⁻¹). Ω·m is the unit of resistivity, which is the reciprocal of conductivity.
Q.299Easy
In a galvanic cell, which electrode acts as the anode?
Answer: B
In a galvanic cell, oxidation occurs at the anode. The anode is the negative electrode where electrons are released.
Q.300Easy
What is the charge on one mole of electrons?
Answer: C
One mole of electrons carries a charge equal to Faraday's constant, which is approximately 96485 C/mol or 96500 C/mol.
