Identify a conjugate acid-base pair in the reaction
NH3+H2O<>NH4^+OH^-

A. H2O and OH^-
B. NH3 and H2O
C. NH3 and OH^-
D. H2O and NH4^+

The correct answer is option A.

Explanation:

According to the Bronsted-Lowry conjugate acid-base theory:

An acid is defined as a substance which looses donates protons and thus forming conjugate base and a base is defined as a substance which accepts protons and thus forming conjugate acid.

For the given chemical equation:

Here, is loosing a proton, thus it is considered as an acid and after losing a proton, it forms which is a conjugate base.

And, is gaining a proton, thus it is considered as a base and after gaining a proton, it forms which is a conjugate acid.

Hence, the correct answer is option A.