Question

What is the conjugate base of \[{H_2}P{O_4}^ - \]?
\[
  A.{H_2}P{O_4} \\
  B.{H_2}P{O_4}^{2 - } \\
  C.{H_3}{O^ + } \\
  D.P{O_4}^{ - 3} \\
 \]

Answer 1

Hint: We can define conjugate base as a base which is formed after an acid loses its hydrogen. Acid has a tendency to donate protons or accept an electron whereas a base has a tendency to accept protons or we can say to donate an electron.

Complete step by step answer:
Let’s start with discussing the conjugate base; conjugate base can be defined as a base which is formed after acid loses its hydrogen. So, whenever acid loses its hydrogen ion the residue that is left is termed as conjugate base as it has a tendency to accept a hydrogen atom or to be more accurate it has a tendency to donate an electron. Acid has a tendency to donate protons or accept an electron whereas a base has a tendency to accept protons or we can say to donate an electron.
Now coming to given question we have to find the conjugate base of the acid \[{H_2}P{O_4}^{2 - }\]
Writing its chemical equation where it loses its \[{H^ + }\] ion and forms a conjugate base is
\[{H_2}P{O_4}^ - \to {H^ + }{\text{ }} + {\text{ }}HP{O_4}^{2 - }\]
As we can see the conjugate base formed is \[HP{O_4}^{2 - }\], which is formed after the acid \[{H_2}P{O_4}^ - \] losses an \[{H^ + }\] ion.

Hence, Option B is the correct answer.

Note:
We must know that the conjugate base and conjugate acid are two components which are formed after the respected acid and base loses their \[{H^ + }\] and \[O{H^ - }\] ions. They gain a tendency to obtain what they have lost, meaning in case of a conjugate base it will try to gain a proton to again become an acid and a conjugate acid will try to gain an electron to again become a base.