Question

After filling the $4d$-orbitals, an electron will enter in:

• A. $4p$
• B. $4s$
• C. $5p$
• D. $4f$

Answer 1

The correct option is C $5p$

After filling the 4d-orbital, an electron will enter in 5p orbital.

The 4d sub-energy level is at a lower energy than the 5p sub-energy level
For 4d, $n=4$ and $l=2$. Hence, $(n+l)=4+2=6$

For 5p, $n=5$ and $l=1$. Hence, $(n+l)=5+1=6$

As the value of $(n+l)$ for 4d orbital is same as that of 5p orbital, 4d orbital is filled before 5p orbital as 4d orbital has lower value of n than 5 p orbital.
Note: If two orbitals have same value of $(n+l)$, then the orbital with lower value of n will be filled first.