Here's why:

* HClO2 is an oxyacid, meaning it contains hydrogen, oxygen, and another non-metal element (chlorine in this case).

* Chlorine in this compound has an oxidation state of +3.

* The suffix "-ous" is used for oxyacids where the non-metal has a lower oxidation state.

Therefore, the name of the compound HClO2 is chlorous acid.