Question

____ series members are radioactive metallic elements.

answer input:
spelling counts but capitalization doesn’t

Explanation:

In chemistry (a subfield of Natural Science), the actinide series (or lanthanide series, but actinide is more associated with radioactive metals) consists of radioactive metallic elements. The actinide series elements are all radioactive, and many are metallic. So the answer is actinide (or lanthanide, but actinide is more precise for radioactive metallic series in this context).

Answer:

actinide