What is the oxidation state of $As$ in $H_{3}AsO_{4}$?

Which one of the following reactions does not involve either oxidation or reduction?

In the following reaction,assign the state for the underlined atom in the product of complete hydrolysis at $R.T.$:
$\underline{Cl_2}O + H_2O \longrightarrow 2HClO$

The oxidation state of sulfur in the anions $SO_3^{2-}$,$S_2O_4^{2-}$,and $S_2O_6^{2-}$ increases in the order:

Which of the following sequences is correct with reference to the oxidation number of iodine?

The oxidation number of nitrogen in $NO_3^-$ is