Conjugate base for Brönsted acids H₂O and HF are:

Concept:

• Acid is a compound that is capable to give hydrogen ions or protons in the solution.
• When the acid donates a hydrogen ion, it becomes a conjugate base.
• Base is the compound that is capable of accepting a hydrogen ion or proton in the solution.
• When a base accepts a hydrogen ion, it becomes a conjugate acid.
• For example, water donates a hydrogen ion to become, OH^-, which is a conjugate base.
• And, water accepts a hydrogen ion to become, H₃O⁺, which is a conjugate acid.

Explanation:

HF on the loss of H+ ion becomes F^- is the conjugate base of HF.

Example : 

Hence, the correct option for the given question is, 3) OH− and F−, respectively.