Final answer:
Sodium (Na) and magnesium (Mg) do not have similar reactive properties. Sodium, with one valence electron, is highly reactive, while magnesium, with two valence electrons, is less so.
Step-by-step explanation:
The chemical reactivity of elements is largely determined by their valence electrons. Elements in the same group often have similar chemical properties because they contain the same number of valence electrons, which governs their behavior in chemical reactions.
The elements sodium (Na) and magnesium (Mg) do not have similar reactive properties despite being in the same period. Sodium, which is an alkali metal, has one valence electron which it can easily lose to form a positive ion. Magnesium, on the other hand, is an alkaline earth metal with two valence electrons and typically forms divalent positive ions. The ease with which sodium gives up its one valence electron makes it highly reactive, particularly with water and halogens. Magnesium's reactivity is more subdued since it needs to lose two electrons to achieve a stable electron configuration.