d- and f-Block Elements Quiz - ICSE Class 12 Chemistry
Free practice quiz: d- and f-Block Elements (ICSE Class 12 Chemistry). 27 multiple-choice questions with answers and explanations. Play online, no sign-up needed.
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The lanthanoid contraction leads to a decrease in atomic radius across the lanthanoid series. Which of the following is a direct consequence of this contraction?
- Increased basicity of oxides
- Decreased ionization energy
- Similar properties of elements following lanthanoids
- Increased metallic character
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Answer: C. Similar properties of elements following lanthanoids
The lanthanoid contraction causes elements in the third transition series (e.g., Hf, Ta, W) to have similar atomic radii and hence similar chemical properties to their corresponding elements in the second transition series (Zr, Nb, Mo). This is due to the poor shielding effect of 4f electrons. Increased basicity of oxides and increased metallic character are generally observed with increasing atomic size, which decreases across the lanthanoids. Ionization energy generally increases across a period.
Consider the following statements regarding the properties of d-block elements: (A) They generally form colored compounds. (B) They exhibit variable oxidation states. (C) They have high enthalpy of atomization. (D) They are poor conductors of heat and electricity.
- A, B, and C are correct, D is incorrect.
- A, B, and D are correct, C is incorrect.
- A, C, and D are correct, B is incorrect.
- All statements A, B, C, and D are correct.
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Answer: A. A, B, and C are correct, D is incorrect.
Statements A, B, and C are true for d-block elements. The ability to form colored compounds (due to d-d transitions), variable oxidation states (due to participation of both ns and (n-1)d electrons), and high enthalpy of atomization (due to strong metallic bonding involving d-electrons) are characteristic features. However, d-block elements are generally good conductors of heat and electricity, making statement D incorrect.
Which of the following compounds of a transition metal is NOT colored?
- KMnO$_4$
- K$_2$Cr$_2$O$_7$
- CuSO$_4 \cdot$ 5H$_2$O
- K$_4$[Fe(CN)$_6$]
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Answer: D. K$_4$[Fe(CN)$_6$]
KMnO$_4$ (permanganate ion) is intensely purple due to d-d transitions in Mn$^{7+}$ (although formally d$^0$, charge transfer transitions are responsible). K$_2$Cr$_2$O$_7$ (dichromate ion) is orange, again due to charge transfer transitions in Cr$^{6+}$. CuSO$_4 \cdot$ 5H$_2$O contains Cu$^{2+}$ ($3d^9$), which exhibits blue color due to d-d transitions. K$_4$[Fe(CN)$_6$] contains Fe$^{2+}$ ($3d^6$) in a complex with cyanide ions. Cyanide is a strong field ligand, leading to a high crystal field splitting energy. In [Fe(CN)$_6$]$^{4-}$, the d-orbitals are all paired up, and the energy gap for d-d transitions is too large for visible light absorption, making the compound pale yellow or practically colorless. The color of potassium ferrocyanide is very faint and often considered colorless in contrast to the others.
The compound that is NOT formed by the oxidation of Cr$^{3+}$ is:
- CrO$_3$
- K$_2$Cr$_2$O$_7$
- CrO$_4^{2-}$
- Cr$_2$O$_3$
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Answer: D. Cr$_2$O$_3$
Cr$_2$O$_3$ is a compound where chromium is in the +3 oxidation state. CrO$_3$ involves Cr$^{6+}$, K$_2$Cr$_2$O$_7$ involves Cr$^{6+}$ (in dichromate ion), and CrO$_4^{2-}$ involves Cr$^{6+}$ (in chromate ion). Therefore, Cr$_2$O$_3$ is not formed by the oxidation of Cr$^{3+}$; rather, it *is* the +3 oxidation state.
Which of the following elements from the d-block exhibits the most pronounced amphoteric nature in its common oxides?
- Vanadium (V)
- Chromium (Cr)
- Manganese (Mn)
- Iron (Fe)
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Answer: B. Chromium (Cr)
Among the given options, chromium exhibits the most pronounced amphoteric behavior in its oxides. For example, CrO is basic, Cr$_2$O$_3$ is amphoteric, and CrO$_3$ is acidic. Vanadium oxides show amphoteric character, but Cr$_2$O$_3$ is a more classic example of an amphoteric oxide among these. Manganese oxides become more acidic with increasing oxidation state (MnO is basic, Mn$_2$O$_3$ is weakly basic/amphoteric, MnO$_2$ is amphoteric, Mn$_2$O$_7$ is acidic). Iron oxides are primarily basic (FeO, Fe$_3$O$_4$) with some amphoteric character in higher oxidation states.