In the periodic table, group 15 all have 5 valence electrons.
The electrons in an atom's outermost shell are called valence electrons because they determine the atom's valency.
The arrangement of elements which are place in a chart where elements are place on the increasing order of atomic number, can be referred as periodic table.
The group 15 elements have 5 valence electrons because 5 electrons are present in the outermost orbital of the each elements that exist in group 15 in the periodic table.
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