Final answer:
In the reaction 2 CuBr → 2Cu + Br2, CuBr is the species that is undergoing reduction as it contains the copper being reduced from an oxidation state of +1 to 0.
Step-by-step explanation:
In the reaction 2 CuBr → 2Cu + Br2, we need to determine which species is undergoing reduction. To do so, we look at the changes in the oxidation states of the elements. Copper (Cu) in CuBr starts with an oxidation state of +1 (because bromine typically has an oxidation state of -1 and the compound is neutral). In the products, Cu is by itself, which means it has an oxidation state of 0. Bromide (Br) in CuBr goes from -1 to 0 in Br2. Since reduction is the gain of electrons, we need to identify the species that is gaining electrons.
Comparing the oxidation states, we see that Cu goes from +1 to 0. It gains an electron, which means it is reduced. Therefore, CuBr is the species that is being reduced because it contains the Cu that is being reduced. Moreover, Br2 is not undergoing reduction; instead, it is being formed from the oxidation of bromide ions (Br-). Therefore, the correct answer to which species is undergoing reduction in the given reaction is option 1) CuBr.