Which of the following is an acid-base reaction?

C(s) + O2(g) CO2(g)

2 HBrO4(aq) + Ba(OH)2(aq) 2 H2O(l) + Ba(BrO4)2(aq)

Cu(s) + 2 AgNO3(aq) 2 Ag(s) + Cu(NO3)2(aq)

MgSO4(aq) + Ba(NO3)2(aq) Mg(NO3)2(aq) + BaSO4(s)

None of these is an acid-base reaction.