19. The atomic number of Bi is 83. What orbital is the highest energy level with electron(s)? (A) 6s (B) 6p (C) 6d (D) 5d

21. Given the following acids and Ka values: HOAc HCN HF HClO₄ 1 x 10⁷ 1.76 x 10⁴ 4.93 x 10⁻¹⁰ 3.53 x 10⁻⁸ Which is correct in term of base strength? (A) CN⁻ < F⁻ < OAc⁻ < ClO₄⁻ (B) CN⁻ < OAc⁻ < F⁻ < ClO₄⁻ (C) ClO4- < OAc- < CN- < F- (D) ClO4- < F- < OAc- < CN-