IUPAC naming of quinol and hydroquinone
Pay attention to the prefix "hydro-", it can definitely change the meaning of the name.

Quinone is the common name given to cyclohexa-2,5-diene-1,4-dione:



However, hydroquinone is not a ketone. Hydroquinone is basically hydrogen added to ketone. As a result, it's not a ketone, but rather it's a phenol.



I must agree, the naming does cause confusion, as this isn't the systematic nomenclature. The common nomenclature doesn't follow any strict rules, and are often named after the compound they were formed from (such as this case). Don't rely on such names too much.