Give the rules for the calculation of oxidation number.

(N/A) $1$. In elements,in the free or uncombined state,each atom bears an oxidation number of $0$. e.g.,$H_{2}, O_{2}, Cl_{2}, N_{2}, Na, Mg, Al, S_{8}, P_{4}$ have an oxidation number of $0$.
$2$. For ions composed of only one atom,the oxidation number is equal to the charge on the ion. e.g.,$Na^{+} = +1, Mg^{+2} = +2, Al^{+3} = +3, Cl^{-} = -1, O^{-2} = -2, F^{-} = -1$.
$3$. Compounds of all alkali metals have an oxidation number of $+1$ and all alkaline earth metals have an oxidation number of $+2$. e.g.,$Na^{+}, K^{+}, Cs^{+}, Rb^{+}, Li^{+}$ and $Mg^{+2}, Ca^{+2}, Be^{+2}, Sr^{+2}$.
$4$. The oxidation number of oxygen in most compounds is $-2$. e.g.,$H_{2}O$ $\rightarrow O^{-2}; CuO$ $\rightarrow O^{-2}$.
Exception: In peroxide compounds,each oxygen atom is assigned an oxidation number of $-1$. e.g.,$H_{2}O_{2}$ $\rightarrow O^{-1}; Na_{2}O_{2}$ $\rightarrow O^{-1}; BaO_{2}$ $\rightarrow O^{-1}$.
$5$. In all its compounds,fluorine has an oxidation number of $-1$. Other halogens $(Cl, Br, I)$ also have an oxidation number of $-1$,except when combined with oxygen in oxoacids and oxoanions,where they have positive oxidation numbers. e.g.,$HClO$ $\rightarrow Cl^{+1}; HClO_{4}$ $\rightarrow Cl^{+7}$.
$6$. The algebraic sum of the oxidation numbers of all the atoms in a neutral compound must be $0$. In a polyatomic ion,the algebraic sum of the oxidation numbers of all atoms must equal the charge on the ion. e.g.,for $(CO_{3})^{-2}$,the sum of oxidation numbers of $C$ and $3O$ must equal $-2$.