This is redox reaction. Redox is when one species reduces, that means gains electrons therefore known as a reduction reaction and the other species oxidises, gives out electrons and thats the oxidation reaction.
For reaction to be complete there should a oxidising species to give out the electrons and a reducing species to gain those electrons.
In the above reaction, Zn(s) gives out electrons therefore its oxidised to Zn2+ (aq) and Cu2+ (aq) gains electrons therefore its reduced to Cu (s).
2 electrons are being transferred so the 2 equations can be combined as it is, since the number of electrons are equal in both reactions.
When the 2 half equations are added, the 2 electrons are cancelled off leaving only the reactants.
the correct answer is 1st response.
