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Explanation:
Sodium (Na) is located in period 3 of the periodic table because it has three electron shells or energy levels.
Periods in the periodic table represent the number of electron shells (or energy levels) that an atom's outermost electrons occupy. Sodium has its outermost electrons in the third energy level, which corresponds to period 3.
Each period in the periodic table begins when a new energy level starts filling with electrons. In the case of sodium, its electron configuration is 1s² 2s² 2p⁶ 3s¹, where the outermost electron is in the 3s orbital, indicating it is in period 3.