GK QUESTION#3337
Which of the following elements is a member of the actinide series?
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Answer
B. Thorium
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Explanation
Thorium, symbol Th and atomic number 90, is an actinide. Lutetium and lanthanum belong to the lanthanide series in its common broad usage, while magnesium is a Group 2 alkaline earth metal. Thus thorium is the actinide among the choices.