Which one of the following chemical equations represent combustion reactions?
B: C+12O2→CO
C: CO+12O2→CO2
The following equations represent reactions used in some important metallurgical processes:
1. Fe3O4+CO(g)→Fe(l)+CO2(g)
2. MgCO3(s)+SiO2(s)→MgSiO3(l)+CO2(g)
3. Au(s)+CN−(aq)+H2O(l)+O2(g)→[Au(CN)2]−(aq)OH−(aq)
Which one (s) represent reduction to a free metal?