Which of the following is existing oxoacid of fluorine?

The only known oxoacid of fluorine is hypofluorous acid, HOF. Due to fluorine's extreme electronegativity, it cannot exhibit positive oxidation states in oxoacids like other halogens. In HOF, fluorine maintains its typical $-1$ oxidation state, hydrogen is $+1$, and oxygen is $0$.

For other compounds such as $\mathrm{HFO}_2$, $\mathrm{HFO}_3$, and $\mathrm{HFO}_4$, fluorine would need to adopt positive oxidation states ($+3$, $+5$, and $+7$ respectively), which contradicts its chemical behavior.

Thus, the correct option is $\boxed{A}$.