16. Which one of the following metal complexes has the slowest water exchange rate? (A) [V(H₂O)₆]³⁺ (B) [Ir(H₂O)₆]³⁺ (C) [Na(H₂O)₆]⁺ (D) [Ca(H₂O)₆]²⁺ (E) [Mn(H₂O)₆]³⁺

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)