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.202Easy
Which of the following elements forms the most stable hydride?
Answer: B
Fluorine forms HF which is the most stable hydride among halogens due to the strong H-F bond (high bond energy ~570 kJ/mol), resulting from fluorine's high electronegativity.
Q.203Medium
The solubility of alkaline earth metal hydroxides increases down the group with the exception of:
Answer: D
Be(OH)₂ is amphoteric and has low solubility. Generally, solubility increases from Mg to Ba, but Be(OH)₂ doesn't follow this trend due to its amphoteric nature.
Q.204Easy
Which of the following oxides is amphoteric?
Answer: B
Al₂O₃ is amphoteric, reacting with both strong acids (forming AlCl₃) and strong bases (forming aluminate ions). Na₂O is basic, SiO₂ is acidic, and P₂O₅ is acidic.
Q.205Medium
The correct order of lattice energies is:
Answer: A
Lattice energy is inversely proportional to the size of ions. As we go from F⁻ to I⁻, ionic size increases, so lattice energy decreases. NaF has the smallest anion, hence highest lattice energy.
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Q.206Easy
Which of the following has the highest electronegativity value?
Answer: B
Fluorine has the highest electronegativity value (4.0 on Pauling scale) among all elements due to its small size and high nuclear charge.
Q.207Medium
In the reaction 2KMnO₄ + 16HCl → 2KCl + 2MnCl₂ + 5Cl₂ + 8H₂O, the reducing agent is:
Answer: B
In this reaction, HCl acts as a reducing agent because Cl⁻ (oxidation state -1) is oxidized to Cl₂ (oxidation state 0). Mn in KMnO₄ is reduced from +7 to +2.
Q.208Easy
Which statement about nitrogen oxides is incorrect?
Answer: C
N₂O₄ is colorless gas, not blue. NO is colorless, NO₂ is brown/reddish-brown, and N₂O is indeed called laughing gas.
Q.209Medium
The thermal stability of Group 16 hydrides decreases in the order:
Answer: A
Thermal stability of hydrides decreases down the group due to decreasing bond strength (H-O > H-S > H-Se > H-Te). The H-O bond is the strongest.
Q.210Medium
Which of the following transition metals can form stable complexes with CO?
Answer: C
Transition metals from 3d, 4d, and 5d series can form stable carbonyl complexes. Examples include Fe(CO)₅, Ni(CO)₄, Mo(CO)₆, and W(CO)₆.
Q.211Medium
The correct order of reducing power of Group 17 hydrides is:
Answer: B
Reducing power increases with increasing size of halogen (decreasing electronegativity). HI is the strongest reducing agent due to the weak H-I bond.
Q.212Hard
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.213Hard
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.214Easy
Which of the following is not a property of noble gases?
Answer: A
Noble gases have VERY HIGH ionization energies (not low) due to their stable electron configuration. All other options are correct properties of noble gases.
Q.215Medium
In the extraction of copper from chalcopyrite (CuFeS₂), the role of silica (SiO₂) is:
Answer: A
SiO₂ acts as a flux. It combines with Fe₂O₃ (formed from iron oxidation) to form iron silicate slag (FeSiO₃), which is removed from molten copper.
Q.216Medium
Which of the following statements about borax (Na₂B₄O₅(OH)₄·8H₂O) is correct?
Answer: B
Borax solution is basic because borate ions undergo hydrolysis: BO₃³⁻ + H₂O ⇌ HBO₃²⁻ + OH⁻, producing OH⁻ ions and making the solution basic.
Q.217Hard
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.218Easy
The coordination number of Cu²⁺ in CuSO₄·5H₂O is:
Answer: B
Cu²⁺ is surrounded by 4 water molecules in the coordination sphere and 2 more from the sulfate ion or additional water molecules, giving octahedral geometry with coordination number 6.
Q.219Easy
Which of the following d-block elements has the configuration [Ar]3d¹⁰4s¹?
Answer: A
Copper has atomic number 29 with configuration [Ar]3d¹⁰4s¹. It exhibits anomalous behavior by having a completely filled d-orbital.
Q.220Easy
The hybridization of sulfur in SF₆ molecule is:
Answer: C
SF₆ has 6 bonding pairs around sulfur with no lone pairs, requiring sp³d² hybridization for octahedral geometry.
