Question

Consider the last electron of an element having atomic number $9$ and choose the correct option.

• A. Sum of total nodes = 1
• B. n = 2; l = 0
• C. Last electron enters in 2s subshell
• D. There are 5e^- with l = 0

Hint:

When determining the quantum numbers, consider the electron configuration and the shell the electron occupies.

Answer 1

The Correct Option is B

Fluorine (F), with atomic number 9, has an electron configuration of \[1s^2 \, 2s^2 \, 2p^5\]. The ninth electron occupies the \( 2p \) orbital.
- For this last electron: - The principal quantum number (\( n \)) is 2, corresponding to the second shell.
- The azimuthal quantum number (\( l \)) is 1, corresponding to a \( p \)-orbital. (Note: The original text incorrectly stated \(l=0\) for a \(p\)-orbital.)
Therefore, the correct quantum numbers for the last electron are \( n = 2; l = 1 \).