Which of the following is not an actinoid?

Terbium

Actinoids are a group of elements that are part of the actinide series in the periodic table, specifically elements with atomic numbers from 89 to 103. They are all radioactive and share similar chemical properties.

The element that is not an actinoid from the given options is (3) Terbium (₆₅Tb). Terbium is not an actinoid; it is a lanthanoid element, which is part of the lanthanide series in the periodic table. Lanthanoids are elements with atomic numbers from 57 to 71.