Which of the following pairs is expected to form colourless compound?

Which of the following pairs is expected to form colourless compound?
  1. $_{57} L a^{3+} \quad{ }_{65} \mathrm{~Tb}^{3+}$
  2. $_{57} L a^{3+} \quad{ }_{71} L u^{3+}$
  3. ${ }_{60} \mathrm{Nd}^{3+} \quad{ }_{61} \mathrm{Pm}^{3+}$
  4. ${ }_{63} \mathrm{Eu}^{3+} \quad{ }_{65} \mathrm{~Tb}^{3+}$

Solution

The configurations of ${ }_{57} \mathrm{La}^{3+}$ is (4f)" while that of ${ }_{\mathrm{I}} \mathrm{Lx}^{3+}$ is $(4 \mathrm{f})^{14}$. They are expected to be
colomicis. ,

Asked in: JEE-TOPICTESTS-CHEMISTRY

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