- A$Al$
- B$As$
- ✓$Ni$
- D$Rb$
Explanation:
The electronic configuration of nickel is $[ Ar ] 3 d ^8 4 s ^2$ which is in sync with the general electronic configuration of a transition element $(n-1) d^{1-10} ns ^2$.
Aluminum, arsenic, and lead don't possess the required configuration so they are not the transition elements.
The electronic configuration of Nickel is $[ Ar ] 3 d ^8 4 s ^2$. So it is a transition element.
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Reason : $\overset{\centerdot \,\,\centerdot }{\mathop{N}}\,{{H}_{2}}$ is more electron donating than $\overset{\centerdot \,\centerdot \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}{\mathop{O{{C}_{2}}{{H}_{5}}}}\,$
Assertion $A$ : Aryl halides cannot be prepared by replacement of hydroxyl group of phenol by halogen atom.
Reason $R$ : Phenols react with halogen acids violently. In the light of the above statements, choose the most appropriate from the options given below:
