Question

Which of the following energy state is filled by an electron after the completion of $4p$ orbital?

• A. $5s$
• B. $3d$
• C. $4d$
• D. $4f$

Answer 1

The correct option is A $5s$

When $4p$ orbital in any atom are filled completely, the next electron goes in $5s(n+l=5+0=5)$ not in $4d(n+l=4+2=6)$,electron first enters into the subshell which is having less $(n+l)$ value (energy). Hence the $5s$ is filled first than $4d$.