The oxidation state of $I$ in $H_4IO_6^-$ is

$2.5 \ mol$ of hydrazine $(N_2H_4)$ loses $25 \ mol$ of electrons to form a new compound $X$. Assuming all lost electrons are contained in the new compound,what is the oxidation state of nitrogen in compound $X$?

Assertion: In some cases,oxygen exhibits a positive oxidation state. Consequently,it is an electronegative element.
Reason: Fluorine is more electronegative than oxygen.

Acidified potassium dichromate is treated with hydrogen sulphide. In the reaction,the oxidation number of chromium

When $K_2Cr_2O_7$ is converted to $K_2CrO_4$,the change in the oxidation state of chromium is

The characteristic oxidation number of atoms in free metals is