MCQ
The outer electronic configuration of $Gd \ (At. \ No. \ 64)$ is
- A$4f^5 \ 5d^4 \ 6s^1$
- ✓$4f^7 \ 5d^1 \ 6s^2$
- C$4f^3 \ 5d^5 \ 6s^2$
- D$4f^4 \ 5d^5 \ 6s^1$
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Assertion $(A):$ The ionic radii of $O ^{2-}$ and $Mg ^{2+}$ are same.
Reason $( R )$ : Both $O ^{2-}$ and $Mg ^{2+}$ are isoelectronic species.
In the light of the above statements, choose the correct answer from the options given below

$(i)\, {CCl_3}^-$ $(ii)\,CCl_2$ $(iii)\, (SiH_3)_2O$ $(iv)\, N(SiH_3)_3$