The characteristic oxidation number of atoms in free metals is

The difference in the oxidation numbers of the two types of sulphur atoms in $Na_2S_4O_6$ is

In which of the following compounds is chlorine in the $+1$ oxidation state?

What is the oxidation state of $Fe$ in $Fe_{0.94}O$?

The oxidation number of $N$ in ${N_2}H_5^+$ is:

Calculate the oxidation number of sulphur,chromium,and nitrogen in $H_2SO_5$,$Cr_2O_7^{2-}$,and $NO_3^-$. Suggest the structures of these compounds and explain the fallacy in the calculated oxidation number for $H_2SO_5$.