Alkali metals, alkaline earth metals, and aluminum all form ions with positive charges equal to
the atomic number.
the group number.
a polyatomic ion.
an ionic bond.

The group number.

The group number in the modern periodic table shows the number of valence electrons (or ions) in the outermost shell of an atom. [The valency is the number of electrons present in the outermost shell that is needed to be eliminated or added from outermost shell of an atom to complete its octate. It is defined for atoms for neutral charges while charge (ions) is defined for charged species].

Therefore, Alkali metals, alkaline earth metals, and aluminum all form ions with positive charges equal to the group number.

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step-by-step explanation: