The conjugate bases of Bronsted acids H₂O and HF are respectively:

1. H₃O⁺ and H₂F⁺, respectively.

2. OH^- and H₂F⁺, respectively.

3. H₃O⁺ and F^-, respectively.

4. OH^- and F^-, respectively.

Which of the following cannot act both as a Bronsted acid and as a Bronsted base?

1. $HC{O}_3^{-}$

2. ${\mathrm{NH}}_3$

3. HCl

4. $HS{O}_4^{-}$