61. Which of the following is the main reason for the complex formation tendency of d-block elements?
A) High electronegativity
B) Low atomic radii
C) Availability of vacant d-orbitals
D) Large ionic radii
Answer: C
Explanation:
The main reason for the complex formation tendency of d-block elements is the availability of vacant d-orbitals. These orbitals can accept electron pairs from ligands, allowing d-block elements to form a variety of coordination complexes.
62. Which of the following pairs of elements shows similar chemical properties due to lanthanide contraction?
A) Zr and Hf
B) Nb and Ta
C) Mo and W
D) Ti and Zr
Answer: A
Explanation:
Zirconium (Zr) and hafnium (Hf) show similar chemical properties due to lanthanide contraction. The lanthanide contraction causes the atomic and ionic radii of Hf to be nearly the same as Zr, leading to similar chemical behavior.
63. Which of the following is true about KMnO4 in acidic medium?
A) It acts as a reducing agent
B) Manganese is reduced to Mn2+
C) Manganese remains in the +7 oxidation state
D) It is colorless in solution
Answer: B
Explanation:
In acidic medium, KMnO4 (potassium permanganate) acts as an oxidizing agent, and manganese is reduced from its +7 oxidation state to Mn2+. This reduction is responsible for the disappearance of the purple color of KMnO4 in solution.
64. Which of the following is a correct statement about the coordination number of a metal in a complex?
A) It is always 4
B) It is the number of ligands attached to the metal
C) It is the charge of the metal ion
D) It is the number of valence electrons in the metal
Answer: B
Explanation:
The coordination number of a metal in a complex refers to the number of ligands attached to the central metal ion. For example, in the complex [Cu(NH3)4]2+, the coordination number of copper is 4.
65. Which one of the following is the most stable oxidation state of cerium?
A) +2
B) +3
C) +4
D) +6
Answer: B
Explanation:
The most stable oxidation state of cerium is +3. Cerium can also exist in the +4 oxidation state, but the +3 state is more stable due to the configuration of its f-electrons.
66. Which one of the following is a property of actinides but not of lanthanides?
A) They form colored compounds
B) They show variable oxidation states
C) They exhibit paramagnetism
D) They are all radioactive
Answer: D
Explanation:
All actinides are radioactive, while only some lanthanides exhibit radioactivity. This property distinguishes the actinides from the lanthanides. Actinides, especially the heavier ones, undergo radioactive decay.
67. In the extraction of copper from copper pyrites, the role of silica is to:
A) Reduce the copper oxide
B) Oxidize the copper sulfide
C) Remove impurities of iron
D) Act as a catalyst
Answer: C
Explanation:
In the extraction of copper from copper pyrites (CuFeS2), silica acts as a flux to remove impurities of iron. Silica reacts with iron oxides to form iron silicate (FeSiO3), which is removed as slag.
68. The main ore of thorium is:
A) Monazite
B) Cassiterite
C) Bauxite
D) Galena
Answer: A
Explanation:
The main ore of thorium is monazite. Monazite is a phosphate mineral that contains rare earth elements and thorium, which is extracted for use in nuclear reactors and other applications.
69. Which of the following is a characteristic of f-block elements?
A) They have high electronegativity
B) They show multiple oxidation states
C) They do not form compounds with non-metals
D) They have no magnetic properties
Answer: B
Explanation:
A characteristic of f-block elements is that they show multiple oxidation states. This is due to the availability of 4f or 5f orbitals, which participate in bonding and allow these elements to exhibit variable oxidation states.
70. Which of the following ions is expected to have the smallest size?
A) Sc3+
B) Fe3+
C) Zn2+
D) Mn2+
Answer: A
Explanation:
Sc3+ (scandium in the +3 oxidation state) is expected to have the smallest size because it has the highest effective nuclear charge for a given number of electrons. This results in a stronger attraction of electrons towards the nucleus, leading to a smaller ionic radius.
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