Different elements are most likely to react in similar ways when they

The elements that has been belonging to the same group have been able to react in similar ways.

The reactivity of the elements has been based on the presence of the valence electrons. The elements that has been belonging to the same group have consisted of the same number of valence electrons with the increase in the number of shells moving from left to right.

Thus, the elements that have been belonging to the same group have consisted of the same reactive properties.

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Belong to the same group.

Explanation:

Different elements are most likely to react in similar ways when they belong to the same group.

This is because the elements in the same group always have similar number of valence electrons which implies that they all have the same number of electrons in their outermost shell. For example,barium (Ba), beryllium (Be), calcium (Ca), magnesium (Mg), radium (Ra), strontium (Sr) all have 2 electrons in their outermost shell and thus they belong to group 2 of elements which are known as Alkaline earth metals and they all tend to react in the same manner with other substances