What is the oxidation state of phosphorus in the phosphate ion $(PO_4^{3-})$?

The equivalent weight of $MnSO_4$ is half of its molecular weight when it is converted into .....

$A$ compound contains atoms $X$,$Y$,and $Z$. The oxidation number of $X$ is $+2$,$Y$ is $+5$ and $Z$ is $-2$. Therefore,a possible formula of the compound is

Assign the oxidation number to the underlined element in each of the following species:
$1$. $NaH_{2}\underline{P}O_{4}$
$2$. $NaH\underline{S}O_{4}$
$3$. $H_{4}\underline{P_{2}}O_{7}$

Write the Lewis structure of the $O_2^-$ ion and find out the oxidation state of each oxygen atom. What is the average oxidation state of oxygen in this ion?

$A$ compound contains three elements $A$,$B$,and $C$. If the oxidation numbers are $A = +2$,$B = +5$,and $C = -2$,the possible formula of the compound is: