Question

The set with correct order of acidity is:
A. $HClO < HCl{O_2} < HCl{O_3} < HCl{O_4}$
B. $HCl{O_4} < HCl{O_3} < HCl{O_2} < HCl{O_{}}$
C. $HClO < HCl{O_4} < HCl{O_3} < HCl{O_2}$
D. $HCl{O_4} < HCl{O_2} < HCl{O_3} < HCl{O_{}}$

Answer 1

We are given four acids. The strength of an acid is directly proportional to the stability of its conjugate base. So first find the stability of conjugate bases of the given acids. The size of an atom or a compound is directly proportional to its stability.

Complete step by step answer:
We are given to find the acidity in increasing order of four acids $HClO,HCl{O_2},HCl{O_3},HCl{O_4}$
An acid is a substance that turns litmus to red and capable of donating a proton.
The conjugate base of an acid is the base member and is able to gain a proton. A conjugate base contains one less hydrogen atom than its acid and one more negative charge than the acid formed it.
Conjugate base of $HClO$ is $Cl{O^{1 - }}$
Conjugate base of $HCl{O_2}$ is $Cl{O_2}^{1 - }$
Conjugate base of $HCl{O_3}$ is $Cl{O_3}^{1 - }$
Conjugate base of $HCl{O_4}$ is $Cl{O_4}^{1 - }$
When the size of a compound or an atom is big then it is more stable i.e. high stability.
In the above four conjugate bases of the acids, the size of $Cl{O_4}^{1 - }$ is more than all other conjugate bases because it contains 3 oxygen atoms, and the size of $Cl{O^{1 - }}$ is less than all other conjugate bases because it has only one oxygen atom. So the conjugate base of $HCl{O_4}$, which is $Cl{O_4}^{1 - }$, is more stable so the acidic strength is higher for $HCl{O_4}$ than other given acids and least for $HClO$.
Therefore, the increasing order of the acidity is $HClO < HCl{O_2} < HCl{O_3} < HCl{O_4}$

Hence we can conclude that option A is correct.

Note:
Another approach.
Acidic strength is directly proportional to the oxidation number of the electronegative element.
In the given acids, the electronegative element is chlorine.
So we have to find the oxidation states of chlorine in all the acids.
In $HClO$, the oxidation state of chlorine is +1.
In $HCl{O_2}$, the oxidation state of chlorine is +3.
In $HCl{O_3}$, the oxidation state of chlorine is +5.