Multiple choice general knowledge science & technology The radio active element series are also known as Lanthanide series True False Reveal answer Fill a bubble to check yourself B Correct answer Explanation The radioactive decay series (uranium series, actinium series, thorium series) are also known as the 'actinide series', not the 'lanthanide series'. Lanthanides are the 15 elements from lanthanum to lutetium and are not radioactive decay series.