Hydrogen iodide (2HI) and chlorine gas (Cl2) combine to form hydrogen chloride (2HCl) and iodine (I2). 2HI + Cl2 ® 2HCl + I2 Iodine is

In hydrogen iodide, iodine has an oxidation state of −1. In iodine gas, I₂, its oxidation state is 0; because iodine’s oxidation state increases from −1 to 0, iodine is oxidized.

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