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# The conjugate base of $H{O^ - }$ is:(A) ${O_2}$(B) ${H_2}O$(C) ${O^ - }$(D) ${O^{2 - }}$ Verified
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Hint: The conjugate base is the negatively charged species obtained when an acid dissociates into its ionic form in the aqueous medium. $H{O^ - }$ can act as an acid as it has a removable proton.

We know that Bronsted-Lowry theory includes the concept of conjugate acids and conjugate bases.
Let’s know what characterizes the conjugate base.
- We know according to Bronsted-Lowry theory that when acid dissolves in aqueous medium, it gets dissociated into proton and a negatively charged ion. This negatively charged ion is termed as a conjugate base of this acid. So, we can write that,
$Acid \to {H^ + } + {\text{Conjugate base}}$
As an example, we can write that when hydrochloric acid dissolves in aqueous media, it dissociates into a proton and chlorine ion, so here chlorine ion is the conjugate base of hydrochloric acid.

Now, we are asked what will be the conjugate base of $H{O^ - }$.
Look, whenever we are being asked to find a conjugate base of some species, then we should accept that a given species would act as an acid and will give a proton when it gets dissociated into aqueous media. So, we can write that dissociation reaction of $H{O^ - }$ in water as:
$H{O^ - } \to {H^ + } + {O^{2 - }}$

Thus it is clear that we will obtain ${O^{2 - }}$ as a negative ion when acid $H{O^ - }$ will get dissociated. So, we can say from the definition of conjugate base that ${O^{2 - }}$ will be the conjugate base of $H{O^ - }$.

So, the correct answer for this question is option (D) ${O^{2 - }}$.

Note:

Do not get confused between conjugate acid and conjugate base. Conjugate acid is a species which is formed when a base accepts a proton. Do not think that as $H{O^ - }$ is a negatively charged species, it cannot act as an acid.

Last updated date: 29th Sep 2023
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