In the reaction in which Zn$^{2+}$ ions formed from Zn atoms take the place of Cu$^{2+}$ ions in CuSO$_4$ and Cu atoms come out, zinc is said to be more reactive than copper. This reaction is a:

1. A more reactive element (Zn) is taking the place of a less reactive element (Cu) in its compound. 2. By definition this single replacement is a displacement reaction. 3. It is not a combining of many reactants into one, nor a single reactant splitting. 4. Double displacement needs two compounds exchanging ions to give a precipitate; only one element is displaced here. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 3 "Chemical Reactions and Equations", p.47_