The element with the highest ionization potential from the elements of period 1, 2 and 3.

Helium

Reason

As ionization potential increases across a period (from left to right) and decreases down a group hence helium will have the highest ionization potential among the elements of period-1, 2 and 3 because it is placed in period 1 and group 18 and is at the top right side of the periodic table.

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