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

The oxidation number of $Fe$ and $S$ in iron pyrites are

Oxidation numbers of $P$ in $PO_4^{3-}$,of $S$ in $SO_4^{2-}$ and that of $Cr$ in $Cr_2O_7^{2-}$ are respectively

What is the oxidation state of $Cr$ in potassium dichromate?

Oxidation number of oxygen in ozone $(O_3)$ is

The oxidation number of an element in a compound is evaluated on the basis of certain rules. Which of the following rules is not correct?
$1$. The oxidation number of hydrogen is always $+1$.
$2$. The algebraic sum of all the oxidation numbers of all elements in a compound is zero.
$3$. An element in the free or the uncombined state bears oxidation number zero.
$4$. In all its compounds,the oxidation number of fluorine is $-1$.