81. Which of the following is not a characteristic property of d-block elements?
A) High melting and boiling points
B) Formation of colored compounds
C) Low density
D) Formation of complex compounds
Answer: C
Explanation:
Low density is not a characteristic property of d-block elements. In fact, many d-block elements are known for their high density, in addition to high melting and boiling points, the formation of colored compounds, and complex compound formation.
82. The lanthanide contraction is responsible for which of the following?
A) Decrease in atomic radii across the lanthanide series
B) Increase in ionic radii across the lanthanide series
C) Decrease in melting points of lanthanides
D) Increase in atomic radii across the lanthanide series
Answer: A
Explanation:
The lanthanide contraction refers to the gradual decrease in atomic and ionic radii across the lanthanide series. This is caused by poor shielding of the 4f electrons, resulting in a stronger attraction of electrons to the nucleus as the atomic number increases.
83. Which of the following is a use of zirconium in industry?
A) As a pigment in white paints
B) As a moderator in nuclear reactors
C) In the production of stainless steel
D) As a catalyst in the Haber process
Answer: B
Explanation:
Zirconium is used as a moderator in nuclear reactors. It is preferred due to its low absorption of neutrons, which helps maintain the controlled chain reactions necessary for the production of nuclear energy.
84. Which of the following ions is expected to have the smallest radius?
A) Zr4+
B) Ti4+
C) Hf4+
D) Ce4+
Answer: C
Explanation:
Hf4+ (hafnium in the +4 oxidation state) is expected to have the smallest radius due to the lanthanide contraction, which causes elements like hafnium to have significantly smaller radii than expected for their position in the periodic table.
85. Which of the following elements is used in the manufacture of permanent magnets?
A) Cerium
B) Neodymium
C) Europium
D) Samarium
Answer: B
Explanation:
Neodymium (Nd) is used in the manufacture of powerful permanent magnets. These neodymium magnets are widely used in electronics, motors, and other applications requiring strong magnetic fields.
86. Which of the following compounds is a common ore of chromium?
A) Hematite
B) Bauxite
C) Chromite
D) Galena
Answer: C
Explanation:
Chromite (FeCr2O4FeCr2O4) is a common ore of chromium. It is the primary source of chromium for the production of stainless steel, alloys, and chrome plating.
87. The oxidation state of iron in Fe(CO)5Fe(CO)5 is:
A) +1
B) +2
C) 0
D) -1
Answer: C
Explanation:
The oxidation state of iron in Fe(CO)5Fe(CO)5 (iron pentacarbonyl) is 0. Carbon monoxide is a neutral ligand, so the oxidation state of iron remains unchanged in this complex.
88. Which of the following oxides of iron is commonly known as rust?
A) Fe2O3
B) FeO
C) Fe3O4
D) FeS2
Answer: A
Explanation:
Fe2O3 (iron(III) oxide) is commonly known as rust when it is hydrated. Rust is a reddish-brown substance formed when iron reacts with oxygen and moisture in the air.
89. Which of the following statements is true for the f-block elements?
A) They are all diamagnetic
B) They exhibit similar chemical properties due to similar ionic radii
C) They show a large variation in their atomic and ionic sizes
D) They have high ionization energies
Answer: B
Explanation:
F-block elements exhibit similar chemical properties because they have similar ionic radii, especially within the lanthanide series, where the ionic radii decrease gradually due to lanthanide contraction. This leads to similar reactivity and chemical behavior.
90. In which of the following oxidation states does uranium exhibit the highest stability in aqueous solution?
A) +3
B) +4
C) +5
D) +6
Answer: D
Explanation:
Uranium in the +6 oxidation state is the most stable in aqueous solutions. In this state, it typically exists as the UO22+ ion (uranyl ion), which is very stable and forms the basis for most uranium chemistry in solution.
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