Which one of the following is NOT a halogen element?

Selenium

The correct answer is option 3. Selenium.

The element that is NOT a halogen from the options provided is Selenium.

Selenium is not a halogen; it is a nonmetal element that belongs to Group 16 (also known as the Oxygen Group or Chalcogens) of the periodic table. Halogens are elements found in Group 17 of the periodic table, which includes fluorine, chlorine, bromine, iodine, and astatine.