Which of the following d-block elements has the configuration [Ar]3d⁵4s¹?
Answer: A
Chromium has the electronic configuration [Ar]3d⁵4s¹ due to half-filled d-orbital stability, making it more stable than [Ar]3d⁴4s².
Q.82Easy
Among the following oxides, which one is amphoteric?
Answer: B
Al₂O₃ reacts with both strong acids and strong bases, exhibiting amphoteric character. MgO is basic, Na₂O is strongly basic, and Cl₂O₇ is acidic.
Q.83Easy
In the extraction of iron from haematite using blast furnace, carbon monoxide acts as:
Answer: A
CO reduces Fe₂O₃ to Fe by accepting oxygen: Fe₂O₃ + 3CO → 2Fe + 3CO₂. CO is the primary reducing agent at higher temperatures.
Q.84Easy
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.85Easy
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.86Easy
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.87Easy
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.88Easy
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.89Easy
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.90Easy
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.91Easy
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.92Easy
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.93Easy
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.94Easy
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.95Easy
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.96Easy
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.97Easy
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.98Easy
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.
Q.99Easy
The Nernst equation relates cell potential to concentration. At 25°C, which form is correct?
Answer: C
The Nernst equation at 25°C is E = E° + (0.0592/n) log Q, where Q is the reaction quotient and n is the number of electrons transferred.
Q.100Easy
Which of the following statements about electrolysis is INCORRECT?
Answer: B
In electrolysis, oxidation occurs at the ANODE, not the cathode. The cathode is where reduction occurs. At the anode, electrons are removed from species.
