Question

Which of the following acid is the strongest acid?

• A. $HClO$
• B. ${HClO}_2$
• C. ${HClO}_3$
• D. ${HClO}_4$

Answer 1

The correct option is D

${\mathrm{HClO}}_4$

Explanation for correct option:

(D) ${\mathbf{HClO}}_{\mathbf{4}}$:

• The oxidation number of the central atom is used to determine an oxyacid's strength.
• The oxyacid becomes more acidic as the oxidation number of the central atom increases.
• The oxidation number of chlorine in each acid is as follows:

$\mathrm{H}\stackrel{+1}{\mathrm{Cl}}\mathrm{O},\mathrm{H}\stackrel{+3}{\mathrm{Cl}}{\mathrm{O}}_2,\mathrm{H}\stackrel{+5}{\mathrm{Cl}}{\mathrm{O}}_3\mathrm{and}\mathrm{H}\stackrel{+7}{\mathrm{Cl}}{\mathrm{O}}_4$

• The order of acidic strength is as follows:

$\mathrm{HClO}<{\mathrm{HClO}}_2<{\mathrm{HClO}}_3<{\mathrm{HClO}}_4$

• Hence, ${\mathrm{HClO}}_4$ is the strongest acid.

So, (D) is the correct option.

Explanation for incorrect options:

(A) $\mathbf{HClO}$:

The oxidation number of Chlorine in $\mathrm{HClO}$ is $+1$. It is the least acidic.

(B) ${\mathbf{HClO}}_{\mathbf{2}}$:

The oxidation number of Chlorine in ${\mathrm{HClO}}_2$ is $+3$. It is more acidic than $\mathrm{HClO}$ but less acidic than ${\mathrm{HClO}}_3$ and ${\mathrm{HClO}}_4$.

(C) ${\mathbf{HClO}}_{\mathbf{3}}$:

The oxidation number of Chlorine in ${\mathrm{HClO}}_3$ is $+5$. It is more acidic than $\mathrm{HClO}$ and ${\mathrm{HClO}}_2$ but less acidic than ${\mathrm{HClO}}_4$

Therefore, the correct option is (D) ${\mathbf{HClO}}_{\mathbf{4}}$.