Question

If Aufbau rule is not obeyed and the electronic filling occurs orbit by orbit till saturation is reached (for a given principal quantum number $n$, electrons are filled in the increasing order of azimuthal quantum number $l$), then the percentage change in sum of all $(n+l)$ values for unpaired electrons in an atom of iron is $10x$. What is the value of $x$?

• A. $5$
• B. $6$
• C. $7$
• D. $3$

Answer 1

The correct option is A $5$

When $n+l$ rule is obeyed, the configuration is

${}^{26}Fe=1s^2,2s^2,2p^6,3s^2,3p^6,4s^2,3d^6.$

Since, $(n+l)$ for each unpaired electron is $5$, so for $4$ unpaired electrons in ${}^{26}Fe$, $(n+l)$ is $5\times 4=20$.

When $n+l$ rule is not obeyed, the configuration is

${}^{26}Fe=1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^8.$

Since, $(n+l)$ for each unpaired electron is $5$, so for $2$ unpaired electrons in ${}^{26}Fe$, $(n+l)$ is $5\times 2=10$.

Now,
% change $=\frac{20-10}{20}\times 100=50=10x$.

$\therefore x=5.$