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H2(g) + I2(g) → 2HI(g)

A student makes the following statements:

Hydrogen always has the same oxidation number, so it has an oxidation number of +1 in both the reactant H2 and product HI.
Iodine is in Group VIIA, so it has an oxidation number of –1 in both the reactant I2 and product HI.
Neither hydrogen nor iodine changes oxidation states, so the reaction is not a redox reaction.
In three to five sentences, describe the mistake that the student made, and determine whether or not the reaction is a redox reaction. Explain your answer.

The student made a mistake in assuming that the oxidation number of hydrogen and iodine remain the same throughout the reaction. In the reactant H2, hydrogen has an oxidation number of +1, while in the product HI, hydrogen has an oxidation number of 0. Similarly, in the reactant I2, iodine has an oxidation number of -1, while in the product HI, iodine has an oxidation number of -2. This change in oxidation number indicates that the reaction is a redox reaction.

The mistake the student made is assuming that oxidation states of elements remain the same throughout the reaction. In reality, the oxidation state of an element can change during a reaction. In this case, hydrogen changes its oxidation state from 0 in H2 to +1 in HI, and iodine changes its oxidation state from 0 in I2 to -1 in HI. This indicates that there is a change in oxidation states, therefore the reaction is a redox reaction.

The student made a mistake in assuming that hydrogen always has the same oxidation number. In reality, the oxidation number of hydrogen can vary depending on the compound it is in. In this reaction, hydrogen goes from an oxidation state of 0 in the reactant (H2) to +1 in the product (HI). On the other hand, iodine goes from an oxidation state of 0 in the reactant (I2) to -1 in the product (HI). Since there is a change in the oxidation states of both hydrogen and iodine, the reaction is indeed a redox reaction.