Classify each of the subsequent reactions as a combination

Question

Classify each of the subsequent reactions as a combination, single replacement, decomposition, double replacement or combustion

2SO2(g)+O2(g)?2SO3(g)

Mg(s)+2AgNO3(aq)?Mg(NO3)2(aq)+2Ag(s)

2KNO3(s)??2KNO2(s)+O2(g)

CuCl2(aq)+2KOH(aq)?Cu(OH)2(s)+2KCl(aq)

2HgO(s)??2Hg(l)+O2(g)

Na2CO3(aq)+BaCl2(aq)?BaCO3(s)+2NaCl(aq)

2FeCl2(aq)+Cl2(g)?2FeCl3(aq)

C4H8(g)+6O2(g)??4CO2(g)+4H2O(g)