Consider the Ka values for the following acids:
Cyanic acid, HOCN, 3.5 × 10⁻⁴
Formic acid, HCHO₂, 1.7 × 10⁻⁴
Lactic acid, HC₃H₅O3, 1.3 × 10⁻⁴
Propionic acid, HC₃H₅O₂, 1.3 × 10⁻⁵
Benzoic acid, HC₇H₅O₂, 6.3 × 10⁻⁵
Which has the weakest conjugate base?