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# The outer electronic configuration of the element Mo (Z=42) is:A.$5{{s}^{2}}4{{d}^{4}}$B.$5{{s}^{1}}4{{d}^{5}}$C.$5{{s}^{2}}5{{p}^{4}}$D.$4{{s}^{2}}3{{d}^{4}}$

Last updated date: 13th Jun 2024
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Hint: Electronic configuration: The distribution of electrons of atoms and molecules in its atomic orbital is termed as Electronic configuration. There are four kinds of atomic orbitals present s, p, f, d. The electrons in atomic orbitals are filled according to order of their increasing energy.

According to Aufbau principle, electronic configuration of $Mo(Z=42)$is:
Electronic Configuration: $1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{2}},3{{p}^{6}},4{{s}^{2}},3{{d}^{10}},4{{p}^{6}},5{{s}^{2}},4{{d}^{4}}$
But, to attain stability the actual electronic configuration of $Mo(Z=42)$is $1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{2}},3{{p}^{6}},4{{s}^{2}},3{{d}^{10}},4{{p}^{6}},5{{s}^{1}},4{{d}^{5}}$ i.e. one electron of s-orbital jumps into d-orbital because half filled orbital is more stable. Now to avoid extra length we convert the electronic configuration to noble gas electronic configuration:$[1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{2}},3{{p}^{6}},4{{s}^{2}},3{{d}^{10}},4{{p}^{6}}],5{{s}^{1}},4{{d}^{5}}$
The outer E. C. is: $[Kr]5{{s}^{1}}4{{d}^{5}}$