Class 12 The d- and f-Block Elements Mock Test (CBSE)

Topics in The d- and f-Block Elements

• Position in the periodic table
• Electronic configurations of the d-block elements
• General properties of transition elements
• Ionisation enthalpies and oxidation states
• Magnetic properties
• Formation of coloured ions and complexes
• Catalytic properties and interstitial compounds
• Potassium dichromate and potassium permanganate
• The lanthanoids
• Lanthanoid contraction
• The actinoids
• Applications of d- and f-block elements

The d- and f-Block Elements practice questions with answers

1. Q1Multiple choice·1 mark
   When an acidic solution of potassium dichromate is treated with hydrogen peroxide ($H_2O_2$), a deep blue-colored complex is formed due to the presence of:

   1. (a)$CrO_5$
   2. (b)$CrO_3$
   3. (c)$Cr_2O_3$
   4. (d)$CrO_4^{2-}$
   Show answer and step marks

   1. Correct option: (a) $CrO_5$. Reaction of acidified dichromate with $H_2O_2$ produces chromium pentoxide ($CrO_5$), which dissolves in organic solvent or remains as a deep blue peroxide complex.+1

   Answer: (a)
2. Q2Multiple choice·1 mark
   Transition metals and their compounds are widely used as catalysts. This property is primarily due to their:

   1. (a)Ability to exhibit variable oxidation states and form complexes
   2. (b)Low melting and boiling points
   3. (c)Inability to form interstitial compounds
   4. (d)Diamagnetic nature and filled d-orbitals
   Show answer and step marks

   1. Correct option: (a) Ability to exhibit variable oxidation states and form complexes. Transition metals show catalytic activity due to their ability to adopt multiple oxidation states and form coordination complexes, providing active sites for reactions.+1

   Answer: (a)
3. Q3Short answer·3 marks
   Give three distinct differences between lanthanoids and actinoids.
   Show answer and step marks

   1. First difference, any one of: lanthanoids show mainly the $+3$ oxidation state (occasionally $+2$, $+4$), whereas actinoids show a wider range ($+3$ to $+7$) because $5f$, $6d$ and $7s$ orbitals have comparable energies; all actinoids are radioactive, whereas among lanthanoids only promethium is; actinoids have a greater tendency to form complexes and form oxo-cations such as $\text{UO}_2^{2+}$; the actinoid contraction from element to element is greater than the lanthanoid contraction due to poorer shielding by $5f$ electrons; lanthanoids fill $4f$ orbitals, whereas actinoids fill $5f$ orbitals; or any other valid difference.+1
   2. Second difference, a different one from the same list.+1
   3. Third difference, a different one from the same list.+1

   Answer: Any three of: lanthanoids show mainly $+3$ while actinoids show $+3$ to $+7$; all actinoids are radioactive but only promethium among lanthanoids; actinoids form complexes and oxo-cations ($\text{UO}_2^{2+}$) more readily; actinoid contraction is greater; lanthanoids fill $4f$, actinoids $5f$ orbitals.

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