Here below some basic MCQ’s about “d and f block elements” with answer which is explained in details. Let’s check one by one.
1. The general electronic configuration of d-block elements is:
A) (n−1)d1−10ns1−2
B) (n−1)d0−1ns2
C) (n−1)d1−5ns2
D) (n−1)d5−10ns1
Answer: A
Explanation:
The general electronic configuration of the d-block elements is (n−1)d1−10ns1−2. These elements have their last electron entering the (n-1)d orbital, while the ns orbital is also occupied. The specific distribution of electrons in d and s orbitals can vary among different elements within the d-block.
2. The color of transition metal complexes is due to:
A) Absorption of light in the infrared region
B) Unpaired electron transitions within the d-orbital
C) Paired electron transitions
D) Crystal field splitting of f-orbitals
Answer: B
Explanation:
The color of transition metal complexes arises due to the absorption of visible light that promotes an electron from one d-orbital to another (d-d transition). This happens because the energy difference between split d-orbitals corresponds to the energy of visible light. The absorbed wavelength corresponds to a particular color, and the complementary color is observed.
3. Which of the following d-block elements is not typically considered a transition metal?
A) Zinc
B) Iron
C) Copper
D) Chromium
Answer: A
Explanation:
Zinc is not considered a transition metal because its dd-orbital is completely filled in both its elemental state and its common oxidation state (+2). Transition metals, by definition, have an incomplete dd-subshell either in their elemental form or in one or more of their oxidation states.
4. Lanthanides and actinides are placed separately in the periodic table because:
A) They are non-metals
B) They belong to f-block elements
C) They have the same properties as transition elements
D) They do not fit into the periodic table
Answer: B
Explanation:
Lanthanides and actinides are placed separately at the bottom of the periodic table because they belong to the f-block elements. Their electrons are progressively filling the (n−2)f(n−2)f-orbitals, which is distinct from the d-block elements where the d-orbitals are filled.
5. Among the following, the compound that shows the highest paramagnetism is:
A) [Co(NH3)6]3+
B) [Fe(CN)6]3−
C) [Cu(NH3)4]2+
D) [Mn(CN)6]3−
Answer: D
Explanation:
Paramagnetism arises due to the presence of unpaired electrons. Manganese in [Mn(CN)6]3− is in the +3 oxidation state with an electronic configuration of 3d4. Since it has four unpaired electrons, it shows the highest paramagnetism among the given compounds.
6. The actinide contraction is greater than lanthanide contraction due to:
A) Greater shielding of 5f orbitals
B) Poorer shielding of 5f orbitals
C) Smaller nuclear charge
D) Smaller size of 5d orbitals
Answer: B
Explanation:
The actinide contraction is greater than the lanthanide contraction because the 5f orbitals in actinides shield the nuclear charge less effectively than the 4f orbitals in lanthanides. As a result, the electrons are more strongly attracted to the nucleus, leading to a greater contraction in atomic and ionic sizes across the actinide series.
7. The oxidation state of chromium in potassium dichromate K2Cr2O7 is:
A) +3
B) +4
C) +6
D) +2
Answer: C
Explanation:
In potassium dichromate, K2Cr2O7, the oxidation state of potassium (K) is +1, and oxygen (O) is -2. The sum of oxidation states in the compound must equal 0. Let the oxidation state of chromium (Cr) be x. We set up the equation: 2(+1)+2x+7(−2)=0 Solving gives x=+6x=+6, so the oxidation state of chromium is +6.
8. The most common oxidation state of lanthanides is:
A) +2
B) +3
C) +4
D) 0
Answer: B
Explanation:
Lanthanides most commonly exhibit an oxidation state of +3. This is because after losing three electrons (two from the 6s orbital and one from the 4f orbital), they attain a stable configuration with a half-filled or empty 4f subshell.
9. Which of the following metals can show a maximum oxidation state of +7?
A) Copper
B) Manganese
C) Iron
D) Cobalt
Answer: B
Explanation:
Manganese can exhibit a maximum oxidation state of +7, as seen in compounds like potassium permanganate (KMnO4). This is because manganese has a total of seven valence electrons that can be lost during oxidation.
10. The magnetic moment of a transition metal ion depends on:
A) The number of paired electrons
B) The number of unpaired electrons
C) Its atomic size
D) Its electron configuration in the outermost shell
Answer: B
Explanation:
The magnetic moment of a transition metal ion is directly related to the number of unpaired electrons. The more unpaired electrons, the greater the magnetic moment. This is typically calculated using the formula: μ=n(n+2)where n is the number of unpaired electrons.
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