Respuesta :
Explanation:
Valence electrons are defined as the electrons that are present in the outermost shell of an atom.
- Helium is the 2nd element of the periodic table having electronic configuration of [tex]1s^2[/tex]
This element has 2 electrons in its outermost shell. So, it has 2 valence electrons. The correct answer is Option B.
- Aluminium is the 13th element of the periodic table having electronic configuration of [tex]1s^22s^22p^63s^23p^1[/tex]
This element has 3 electrons in its outermost shell. So, it has 3 valence electrons. The correct answer is Option C.
- Fluorine is the 9th element of the periodic table having electronic configuration of [tex]1s^22s^22p^5[/tex]
This element has 7 electrons in its outermost shell. So, it has 7 valence electrons. The correct answer is Option D.
- Sodium is the 11th element of the periodic table having electronic configuration of [tex]1s^22s^22p^63s^1[/tex]
This element has 1 electron in its outermost shell. So, it has 1 valence electron. The correct answer is Option A.