18. How many unpaired electrons are found in [Dy(H₂O)₆]³⁺? (A) 3 (B) 4 (C) 5 (D) 6 (E) 7

1. The Nobel Prize in Chemistry in 2022 was awarded to click chemistry, or the azide-alkyne cycloaddition to connect two molecular fragments. For their initial discovery, what metal ion was required as a catalyst for this reaction to proceed at a milder condition? (A) Cu(I) (B) Zn(II) (C) Fe(II) (D) Fe(III) (E) Mo(II)