The oxidation number of nitrogen in $NH_2OH$ is

Write the oxidation number of the carbon atom in the carboxyl group of acetic acid $(CH_3COOH)$.

The difference in oxidation state of chromium in chromate and dichromate salts is $....$ .

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 number of iodine varies from:

The oxidation state of sulphur in $H_2S_2O_7$ is