20. The C-C σ bond of H2C=CH2 is formed by two orbitals. What are these orbitals? (A) s and s (B) s and sp2 (C) s and sp3 (D) sp2 and sp2

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-