Which period of the periodic table contains the element helium?
A
Period 2
B
Period 1
C
Period 4
D
Period 3
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1
Recall that the periodic table is arranged in periods (rows) and groups (columns), where each period corresponds to the principal energy level (n) of the valence electrons.
Identify the position of helium (He) on the periodic table. Helium is located in the top right corner of the table, in the first row.
Understand that the first period contains only two elements: hydrogen (H) and helium (He), corresponding to the filling of the 1s orbital.
Recognize that helium belongs to Period 1 because its electrons occupy the first principal energy level (n=1).
Conclude that the correct period for helium is Period 1.