Question
Answer the following questions:
a. The figure given alongside illustrates the first ionization enthalpies of first, second and third series of transition elements. Answer the question that follows:
b. Which series amongst the first, second and third series of transition elements have the highest first ionization enthalpy and why?
c. Separation of lanthanoid elements is difficult. Explain.
d. $Sm ^{2+}, Eu ^{2+}$ and $Yb ^{2+}$ ions in solutions are good reducing agents but an aqueous solution of $Ce ^{4+}$ is a good oxidising agent. Why?

Answer

a. Third series has the highest first ionization energy due to poorest shielding effect of the fully filled 4 fsubshell.
b. This is due to lanthanoid contraction.
c. $Sm ^{2+}, Eu ^{2+}$ and $Yb ^{2+}$ ions are good reducing agents as they tend to acquire common oxidation state of +3 shown by lanthanoids by the loss of one electron while $Ce ^{4+}$ gains one electron to attain +3 . Hence, $Ce ^{4+}$ is an oxidising agent.

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