The oxidation state of $\text{Cr}$ in ${\text{CrO}}_5$ is:

Chromium pentoxide (${\text{CrO}}_5$) has a "butterfly" structure. It contains one $\text{Cr=O}$ bond and two peroxide ($-\text{O-O}-$) linkages.Oxygen in $\text{Cr=O}$ has an oxidation state of $-2$.The four oxygens in peroxide bonds each have an oxidation state of $-1$.Let $x$ be the oxidation state of $\text{Cr}$:$x+1(-2)+4(-1)=0⟹x-2-4=0⟹x=+6$.