What is the oxidation number of $S$ in $SO_3^{2-}$?

In how many of the following compounds of sulphur,the oxidation state of sulphur atom is $+6$?
$H_2S_2O_8, H_2SO_5, H_2SO_3, H_2SO_4, H_2S_2O_7, SO_2Cl_2, SOCl_2$

Sulphur has the lowest oxidation number in

In which of the following compounds is the oxidation state of $N$ the highest?

Which of the following involves the transfer of five electrons?

The oxidation state of iodine in $I_3^{-}$ is: