(a)  Decomposition reaction as well as displacement reaction(a) Combination reaction as well as double displacement reaction (b) Redox reaction as well as displacement reaction (c) Double displacement reaction as well as Redox reaction

Option(c) is the answer. Redox reaction as well as displacement reaction takes place because magnesium get oxidized here and copper reduces. Therefore it is reduction and magnesium displaces copper in the solution as being more reactive. Thus becomes displacement reaction