72. Which one of the following ions has the largest number of unpaired electrons?
A) Fe2+
B) Mn2+
C) Cr3+
D) Co2+
Answer: B
Explanation:
Mn2+ (manganese in the +2 oxidation state) has five unpaired electrons in the 3d5 configuration, which is the maximum number of unpaired electrons possible in a d-block element in the +2 oxidation state.
73. Which of the following lanthanides is known for its ability to absorb neutrons and is used in nuclear reactors?
A) Samarium
B) Dysprosium
C) Neodymium
D) Gadolinium
Answer: D
Explanation:
Gadolinium (Gd) is known for its ability to absorb neutrons and is used in nuclear reactors as a control material. It has a high neutron absorption cross-section, making it effective in controlling nuclear reactions.
74. Which of the following is the strongest oxidizing agent?
A) MnO4−
B) Cr2O72−
C) ClO4−
D) NO3−
Answer: A
Explanation:
MnO4− (permanganate ion) is the strongest oxidizing agent among the options. In acidic conditions, MnO4− is reduced to Mn2+, and this reduction releases a large amount of energy, making it a powerful oxidizer.
75. Which of the following transition elements shows the highest melting point?
A) Titanium
B) Chromium
C) Iron
D) Tungsten
Answer: D
Explanation:
Tungsten (W) has the highest melting point of all transition metals, around 3422°C. This property makes it useful in applications where high-temperature resistance is required, such as in filaments for light bulbs and heating elements.
76. In which of the following processes is vanadium pentoxide (V2O5) used as a catalyst?
A) Contact process
B) Haber process
C) Solvay process
D) Ostwald process
Answer: A
Explanation:
Vanadium pentoxide (V2O5 is used as a catalyst in the contact process for the production of sulfuric acid. It catalyzes the oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3).
77. Which of the following statements is correct for the d-block elements?
A) They are all non-metals
B) They show a wide range of oxidation states
C) They do not form colored compounds
D) They are poor conductors of electricity
Answer: B
Explanation:
D-block elements show a wide range of oxidation states due to the involvement of their d-electrons in bonding. This is one of the key characteristics of transition metals, leading to diverse chemical properties and the formation of coordination complexes.
78. Which of the following is used as a moderator in nuclear reactors?
A) Lead
B) Graphite
C) Thorium
D) Beryllium
Answer: B
Explanation:
Graphite is used as a moderator in nuclear reactors. Moderators slow down fast neutrons, making them more effective in sustaining a controlled nuclear chain reaction.
79. The color of Cr3+ ions in aqueous solution is:
A) Yellow
B) Green
C) Red
D) Blue
Answer: B
Explanation:
Cr3+ ions in aqueous solution are typically green in color. The color arises due to d-d transitions, where electrons move between energy levels within the d-orbitals in the presence of ligands such as water molecules.
80. Which of the following is an actinide element?
A) Lutetium
B) Thorium
C) Gadolinium
D) Ytterbium
Answer: B
Explanation:
Thorium (Th) is an actinide element. Actinides are f-block elements that include elements with atomic numbers from 89 to 103, and thorium is one of the lighter actinides, used in nuclear reactors.
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