The oxidation number of fluorine in $F_2O$ is

What is the oxidation number of oxygen in $OF_2$?

The compound $YBa_2Cu_3O_7$,which shows superconductivity,has copper in an oxidation state of ........ Assume that the rare earth element Yttrium is in its usual $+3$ oxidation state.

When $KMnO_4$ is reduced with oxalic acid in acidic solution,the oxidation number of $Mn$ changes from

What is the change in the oxidation state of $Mn$ in the reaction of $MnO_4^{-}$ with $H_2O_2$ in acidic medium?

Compounds having the highest oxidation state of the central atom act as acids,the lowest ones act as bases,and intermediate oxidation states act as amphoteric. Which one of the following is amphoteric?