Question

question 6
listen
what do the electron configurations for fluorine, chlorine, and bromine have in common?
a they all end in $p^5$.
b they all end in $s^2$.
c they all have valence electrons in energy level 4 ($n = 4$).

Explanation:

Fluorine (F), chlorine (Cl), and bromine (Br) are halogens (Group 17 elements). The electron configuration of fluorine is $1s^2 2s^2 2p^5$, chlorine is $1s^2 2s^2 2p^6 3s^2 3p^5$, and bromine is $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5$. All end with $p^5$ (valence shell p - subshell has 5 electrons). Option B is incorrect as they don't end with $s^2$. Option C is incorrect: fluorine's valence electrons are in $n = 2$, chlorine in $n = 3$, bromine in $n = 4$, so they don't all have valence electrons in $n = 4$.

Answer:

A. They all end in $\boldsymbol{p^5}$.