Answer:
See detailed explanation.
Explanation:
Hello.
In this case, since the electron configuration of potassium whose atomic number is 19 turns out:
[tex]K^{19}: 1s^2,2s^2,2p^6,3s^2,3p^6,4s^1[/tex]
We can see that the last level is 4 which has one electron, meaning that potassium has one valence electron. Moreover, since bromine's atomic number is 35, its electron configuration is:
[tex]Br^{35}: 1s^2,2s^2,2p^6,3s^2,3p^6,4s^2,3d^{10},4p^5[/tex]
We can see that the last level is also 4 and it has 2+5 = 7 valence electrons. In such a way, we infer that the valence electrons are computed by the electrons at the outer or last energy level of an element.
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