Question

What is the conjugate base of $N{H_3}$ .

Answer 1

The concept of conjugate acid or base comes from the Bronsted-Lowry acid base theory. Thus basic nature does not depend upon the ability to release or donate hydroxide ions or lone pairs of electrons present on the nitrogen atom of ammonia.

Complete answer:
According to the Bronsted-Lowry acid base theory, the compounds that donate or release hydrogen ions are said to be acidic and the ones that accept the hydrogen ions are considered basic in nature.
When an acid-base reaction takes place between a Bronsted-Lowry acid and a Bronsted-Lowry base than the species formed after accepting the proton from the acid is known as conjugate base and the species left after removal of a proton is known as a conjugate acid. Thus the conjugate acid-base pairs are compounds with almost the same molecular formula which is the only difference of a proton.
Lose of protons from any compound makes it negatively charged and if a proton is accepted then the neutral compound becomes positively charged. The magnitude of charge depends upon the number of protons being lost or accepted in the reaction. For each proton transfer there is a unit charge difference.
In order to determine the conjugate base of ammonia $(N{H_3})$ , it should be treated as a Bronsted-Lowry acid. Thus ammonia loses a proton to produce an amide anion. The reaction can be written as follows:
$N{H_3} \rightleftharpoons {H^ + } + N{H_2}^ -$
Thus the conjugate base of ammonia is amide anion $(N{H_2}^ - )$ .

Note:
Ammonia is an amphoteric compound according to the Bronsted-Lowry acid base theory as it is capable of both accepting as well donating or releasing hydrogen ions. It behaves like an acid in presence of a stronger base and a base in the presence of a stronger acid.