To determine which base is the weakest among the given options, we need to consider their ability to accept protons (H⁺) based on their conjugate acids’ strengths.
- F⁻ (Fluoride ion): The conjugate acid is HF, which is a weak acid. This means F⁻ can act as a relatively strong base.
- NH₃ (Ammonia): The conjugate acid is NH₄⁺ (ammonium), which is also a weak acid. NH₃ is a moderate base.
- OH⁻ (Hydroxide ion): The conjugate acid is H₂O (water), which is a neutral substance. OH⁻ is considered a strong base.
- SO₄²⁻ (Sulfate ion): The conjugate acid H₂SO₄ is a strong acid, indicating that SO₄²⁻ is a very weak base.
- C₂H₃O₂⁻ (Acetate ion): The conjugate acid is CH₃COOH (acetic acid), which is a weak acid, making C₂H₃O₂⁻ a moderate base.
Comparing these bases, SO₄²⁻ has the strongest conjugate acid, which corresponds to being the weakest base. Therefore, among the given options, the weakest base is: