Answer:
B) are in the same period of elements.
Explanation:
<em>The elements sodium, magnesium, and silicon
</em>
<em>A) are isotopes of each other
.</em> NO. Isotopes are 2 or more forms of the same element, with a different number of neutrons.
<em>B) are in the same period of elements.</em> YES.
Let's consider the electron configuration of these elements.
₁₁Na 1s² 2s² 2p⁶ 3s¹
₁₂Mg 1s² 2s² 2p⁶ 3s²
₁₄Si 1s² 2s² 2p⁶ 3s² 3p²
Since the valence electrons are in the level 3, they all belong to the third period in the periodic table.