Which of these conjugate acid-base pairs will not function as a buffer?
a. hno3 and no3−
b. hco3− and co32−
c. c2h5cooh and c2h5coo−

HNO₃ and NO³⁻ would not function as buffer

Explanation:

The buffer solution are usually prepared by using  any  weak acid (which would partially dissociate)  and mixing this weak acid with its own conjugate base or any weak base (which would partially dissociate) and mixing with  with its conjugate acid.

A buffer solution is a solution which resists change in pH of the solution.

Since nitric acid is a very strong acid and hence neither nitric acid HNO₃ or its conjugate base NO³⁻ anionb is suitable for the preparation of buffer solution.

HCO³⁻ is a weak  acid and hence it can form a buffer solution with its conjugate base CO₃²-. so they can be used to form buffer.

C₂H₅COOH is a weak acid and hence it can also form buffer solution with its conjugate base.

So only HNO₃and NO³⁻ would not be able to form buffer

So option a is the answer.