Question

Which of the following is the strongest acid?
A. $Cl{O_3}(OH)$
B. $Cl{O_2}(OH)$
C. $SO{(OH)_2}$
D. $S{O_2}{(OH)_2}$

Answer 1

Hint: Perchloric acid is the strongest acid with molecular formula, $Cl{O_3}(OH)$. Compared to all the given choices, perchloric acid shows the highest oxidation number on chlorine or the central atom.

Complete step by step answer:
When we say a strong acid, we refer to its tendency to lose hydrogen readily. Now when the central atom, $Cl$ and $S$ in the above examples have different oxidation states, the readiness of the hydrogen atom to break from the molecule depends on the positivity of the oxidation number of the central atom. In option C, it is just a weak mixture of sulphur dioxide and water to form an aqueous solution known as sulphurous acid. It is a weak acid. Option D is the most popular sulphuric acid and the oxidation number of sulphur is +6. In option B, the oxidation number of chlorine is +5 and in case of option A, the oxidation number of chlorine is +7. Thus the $O - H$ bond is the weakest in perchloric acid in option A and thus it is our answer to strongest acid. It is stronger than most popular nitric acid also.
So, the correct answer is “Option A”.

Note: Perchloric acid is considered to be highly corrosive in nature and it is useful in rocketry for its potentially explosive mixtures. We can also say that there are three atoms of oxygen and these will attract the electrons of $O - H$ towards oxygen and make the bond weaker.