Answer : The option (d) is not a conjugate acid-base pair.
Explanation :
According to the Bronsted Lowry concept, Bronsted Lowry-acid is a substance that donates one or more hydrogen ion in a reaction and Bronsted Lowry-base is a substance that accepts one or more hydrogen ion in a reaction.
Or we can say that, conjugate acid is proton donor and conjugate base is proton acceptor.
(a) The equilibrium reaction will be,
In this reaction, are act as a conjugate acid-base.
(b) The equilibrium reaction will be,
In this reaction, are act as a conjugate acid-base.
(c) The equilibrium reaction will be,
In this reaction, are act as a conjugate acid-base.
(d) The equilibrium reaction will be,
In this reaction, are act as a conjugate base-acid.
Hence, from this we conclude that, the option (d) is not a conjugate acid-base pair but it is a act as conjugate base-acid.