Find the oxidation number of $Cl$ in $ClO_4^-$

Consider the following molecules: $Br_3O_8$,$F_2O$,$H_2S_4O_6$,$H_2S_5O_6$,and $C_3O_2$. Count the number of atoms existing in their zero oxidation state in each molecule. Their sum is . . . . .

If a metal ion $M^{3+}$ loses three more electrons,what will be its final oxidation number?

What are the oxidation numbers of the underlined elements in each of the following and how do you rationalize your results?
$(1)$ $K\underline{I_3}$
$(2)$ $H_2\underline{S_4}O_6$
$(3)$ $\underline{Fe_3}O_4$
$(4)$ $\underline{C}H_3\underline{C}H_2OH$
$(5)$ $\underline{C}H_3\underline{C}OOH$

How many peroxide groups are present in $CrO_5$?

In the conversion $Br_2 \to BrO_3^-$,the oxidation state of bromine changes from