19. Determine the ground state free-ion term symbol (²s⁺¹Lⱼ) of Dy³⁺. (A) ⁶H₁₅/₂ (B) ⁸S₇/₂ (C) ⁵H₄ (D) ³H₄ (E) ⁶H₅/₂

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)