Among all the 14 elements of the lanthanoid series, exactly how many elements are strictly classifie — d and f Block Elements Chemistry Question

💡 Solution & Explanation

Unlike the actinoid series where every element is radioactive, the lanthanoid series is mostly stable. The sole exception is Promethium ($Pm$, $Z=61$), which is a synthetically produced radioactive element. Therefore, only $1$ lanthanide is radioactive.