# How to determine the strongest oxyacid of chlorine?

Which is the strongest acid here?

• $\ce{HClO}$
• $\ce{HClO2}$
• $\ce{HClO3}$
• $\ce{HClO4}$

I found this question, didn't really get the first answer, but this one in particular seemed interesting.

Apparently, you calculate a $\mathrm{p}K_\mathrm{a}$ for each substance.

According to this website.

$$\mathrm{p}K_\mathrm{a} = -\log_{10}K_\mathrm{a}$$

I need to find out $K_\mathrm{a}$ then. From what I understand $K_\mathrm{a}$ is obtained from dividing the concentrations of products by the concentrations of reagents. However, how am I supposed to do so if I am not given any equilibrium reactions?