JAMB Chemistry 2021 Paper

Concept:Elements following actinium in the periodic table belong to the actinoid series.Explanation:The actinoid series includes elements with atomic numbers from $89$ to $103$.Actinium has atomic number $89$, so the fourteen elements after it run from atomic number $90$ to $103$.These fourteen elements are thorium ($90$) through lawrencium ($103$).The series is named after actinium, the first element in the group, and the elements are collectively called actinoids.Answer:A. Actinoids.