Question:

The d-electron configurations of Cr2+,Mn2+,Fe2+Cr^{2+},Mn^{2+},Fe^{2+} and Co2+Co^{2+} are d4,d5,d6d^4, d^5, d^6 and d7d^7 respectively. Which one of the following will exhibit the lowest paramagnetic behaviour? (Atomic no. Cr=24,Mn=25,Fe=26,Co=27Cr=24, Mn=25, Fe=26, Co=27).

Updated On: Jul 29, 2022
  • [Co(H2O)6]2+][Co(H_2O)_6]^{2+}]
  • [Cr(H2O)6]2+][Cr(H_2O)_6]^{2+}]
  • [Mn(H2O)6]2+][Mn(H_2O)_6]^{2+}]
  • [Fe(H2O)6]2+][Fe(H_2O)_6]^{2+}]
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The Correct Option is A

Solution and Explanation

\therefore Since Co2+Co^{2+} has lowest no. of unpaired electrons hence lowest paramagnetic behaviour is shown by [Co(H2O)6]2+[Co(H_2O)_6]^{2+}
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Concepts Used:

Properties of D Block Elements

  • Multiple oxidation states- The oxidation states of d block elements show very few energy gaps; therefore, they exhibit many oxidation states. Also, the energy difference between s and d orbital is very less. Therefore both the electrons are involved in ionic and covalent bond formation, which ultimately leads to multiple oxidation states.
  • Formation of complex compounds- Ligands show a binding behavior and can form so many stable complexes with the help of transition metals. This property is mainly due to:
    • Availability of vacant d orbitals.
    • Comparatively small sizes of metals.
  • Hardness- Transition elements are tough and have high densities because of the presence of unpaired electrons.
  • Melting and boiling points- Melting and boiling points of transition are very high because of the presence of unpaired electrons and partially filled d orbitals. They form strong bonds and have high melting and boiling points.
  • Atomic radii- The atomic and ionic radius of the transition elements decreases as we move from Group 3 to group 6. However, it remains the same between group 7 and group 10, and from group 11 to group 12 increases.
  • Ionization enthalpy- The ionization enthalpies of the transition elements are generally on the greater side as compared to the S block elements