Which among the following is NOT a metal?

selenium

The correct answer is option 4. selenium.

Among the options provided, selenium is NOT a metal.

Selenium is a nonmetal element, specifically a metalloid, that exhibits properties intermediate between those of metals and nonmetals. It is located in Group 16 of the periodic table, also known as the oxygen group or chalcogens. Selenium is commonly used in electronic devices, solar cells, and photocopiers, among other applications.