Question

The incorrect electronic arrangement is

• A. 2, 8, 13, 1
• B. 2, 8, 12, 2
• C. 2, 8, 8, 1
• D. 2, 8, 8, 2

Hint:

If the outermost shell contains electrons, the shell just before it should not have more than \textbf{8 electrons}.

Answer 1

The Correct Option is A

Step 1: Recall the Bohr–Bury rules for electronic configuration:

Maximum electrons in a shell = $2n^2$.
The outermost shell can have a maximum of 8 electrons.
The penultimate shell can have a maximum of 18 electrons, but if the outermost shell has electrons, the penultimate shell cannot have more than 8 electrons.

Step 2: Examine option (A): $2, 8, 13, 1$ Here, the outermost shell has 1 electron, but the penultimate shell has 13 electrons, which violates the Bohr–Bury rule.
Step 3: Check the remaining options:

(B) $2, 8, 12, 2$ — valid as per Bohr–Bury rules.
(C) $2, 8, 8, 1$ — valid.
(D) $2, 8, 8, 2$ — valid.

Step 4: Therefore, the incorrect electronic arrangement is 2, 8, 13, 1.