What is the change in oxidation number of an atom of iodine in the half-reaction I ^- (aq) → I2 (s)?
a) an decrease of 1
b) a increase of 1
c) an decrease of 2
d) a increase of 2
e) an decrease of 3
The oxidation number of iodine in I^- (aq) is -1. In I2 (s), the oxidation number of iodine is 0 because it is in its elemental form. Therefore, there is an increase in the oxidation number of iodine by 1.
The correct answer is b) an increase of 1.