In each group, name any answer which matches the first category to reveal the second category, then name any answer which applies to both categories to reveal a third, and so on.
I was super lucky and guessed that element at the second step - no idea why it was the first of the 13 possibilities to come to mind. Really fun quiz. Would love to see more periodic table quizzes.
Actinides or Lanthanides. I made some lucky guesses.