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The d & f Block Elements — Chemistry STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceChemistryThe d & f Block Elements5 Marks
Question
  1. With reference to structural variability and chemical reactivity, write the differences between lanthanoids and actinoids.
  2. Name a member of the lanthanoid series which is well known to exhibit $+4$ oxidation state.
  3. Complete the following equation:
$\text{MnO}_{4}^{-}+\text{8H}^{+}+\text{5e}^{-}\rightarrow$
  1. Out of $Mn^{3+}$ and $Cr^{3+}$, which is more paramagnetic and why?
$($Atomic nos: $Mn = 25, Cr = 24).$
✓

Answer

  1.  
Lanthanoids
Actinoids
Atomic/ionic radii does not show much variation $+3$ is the most common oxidation state, in few cases $+2 \& +4.$
Atomic/ionic radii show much variation/Besides $+3$ oxidation state they exibit $+4,+5,+6,+7$ also.
They are quite reactive.
Highly reactive in finely divided state.
  1. Cerium $(Ce^{4+}).$
  2. $\text{MnO}_{4}^{-}+\text{8H}^{+}+\text{5e}^{-}\rightarrow\text{Mn}^{2+}+\text{4H}_{2}\text{O}$.
  3. $Mn^{3+}$​​​​​​​ is more paramgnetic.
Because $Mn^{3+}$ has $4$ unpaired electrons $(3d^4)$ therefore more paramagnetic whereas $Cr^{3+}$ has $3$ unpaired electrons $(3d^3).$

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