What is the oxidation number of oxygen in a superoxide ion?

In which of the following species is the oxidation number of iodine fractional?

Calculate the oxidation number of nitrogen and chlorine in $NOClO_4$.

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.

$A$ compound contains atoms of $x, y$ and $z$ elements. Oxidation numbers of $x, y$ and $z$ are $+3, +5$ and $-2$ respectively. Identify the possible formula of this compound?

What are the oxidation numbers of nitrogen in $NH_4NO_3$?