Concept:Oxidation number shows the loss or gain of electrons by an element during a reaction.
Explanation:In
Cu2S, sulfur has an oxidation number of
−2.
Since the compound is neutral, the total oxidation number of two copper atoms is
+2.
Therefore, each copper atom has an oxidation number of
+1.
On the product side, copper exists as a free element,
Cu(s).
The oxidation number of any free element in its elemental state is
0.
So copper changes from
+1 in the reactant to
0 in the product.
Thus, the oxidation number of copper decreases from
+1 to
0.
Answer:A.
+1 to
0