What is the oxidation state of $S$ in $SO_4^{2-}$?

Assertion: The average oxidation number of sulfur in $Na_2S_4O_6$ is $2.5$.
Reason: Two $S$ atoms are not directly bonded to $O$-atoms.

What is the oxidation state of $Fe$ in $Fe_3O_4$?

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

The oxidation states of $Cr$ in $K_2Cr_2O_7$ and $CrO_5$ are,respectively:

Fill in the blanks:
$(1)$ Oxidation number of $Cr$ in $Na_3Cr_3O_{10}$ is ........
$(2)$ Oxidation number of $H$ in lithium aluminum hydride $(LiAlH_4)$ is .......
$(3)$ Oxidation number of oxygen in potassium ozonide $(KO_3)$ is .........
$(4)$ Oxidation number of $C$ in fullerene and graphite is .......