Answer:
A. They possess the same number of outermost electrons. is the correct answer.
Explanation:
elements in a vertical column of the periodic table have similar chemical properties because they possess the same number of outermost electrons.
outermost electrons are also named as valence electrons.
Electrons define the chemical reactivity of the element, that the reason elements in a similar group have an equal number of electrons in the outermost orbital, providing them with similar chemical properties.
