Question

Which among the following is the strongest acid?
A. HOCl
B. HClO$_2$
C. HClO$_3$
D. HClO$_4$

Answer 1

Hint: The given options are the oxoacids. The acidity order is based on the Lowry-Bronsted concept. Look for the stability of conjugate bases, the conjugate base with the minimum stability will be the least acidic in nature. So, now the strongest acid can be determined.

Complete step by step answer:
Now, first let us discuss the Lowry-Bronsted concept. We know that a strong acid is composed of weak conjugate base, whereas weak acid is composed of strong conjugate base.
In the given options, we will write the conjugate bases i.e. ClO$^{-}$, ClO$_2$ $^{-}$, ClO$_3$ $^{-}$, and ClO$_4$ $^{-}$.
So, we can write the order of charge stabilisation, i.e.
ClO$^{-}$ < ClO$_2$ $^{-}$ < ClO$_3$ $^{-}$ < ClO$_4$ $^{-}$
Now, the first option is HOCl. The conjugate base has the minimum stability, and it means that it depicts the maximum attraction for hydrogen ion.
So, we can say that HOCl will be least acidic.
The second option we have HClO$_2$. Here, it will be more acidic than the first one, but least acidic than the other two as the charge stabilisation is increasing as mentioned in the order above.
The third option we have is HClO$_3$. Now, it will be more acidic than the first two, but least than the last one.
Talking about the fourth one i.e. HClO$_4$. Here, the conjugate base is the weakest one, and we can say it is maximum stabilised.
So, we can say it is the strongest acid.
In the last we can conclude that the strongest acid is HClO$_4$.
Hence, the correct option is (D).

Note:
Don’t get confused about why the conjugate base i.e. the strongest one is minimum stabilised, and vice-versa. Then, in consideration with the Lowry-Bronsted concept, the weaker base will have the least attraction for hydrogen ions. So, we can say that a conjugate base with minimum stability, will be the stronger base, and the least acidic in nature.