How many electrons are lost or gained in forming each #Cu^(2+)#?
Suppose you knew nothing about chemistry, but something about physics and electrical charge. You know that if something is neutral then it has an equal number of positive and negative charges. In the reaction above, we started with a neutral atom (copper metal), and upon (so-called) oxidation we finished with a cupric ion,
In every chemical reaction, 2 things are conserved: (i) mass; and (ii) charge. Is mass conserved in every nuclear reaction?