Question

combustion reaction produce carbon dioxide and water so

Is magnesium + oxygen -------> magnesium oxide

a combustion reaction if yes then why heat , water and co2 didn't produce

Answer 1

2Mg(s)+O2(g)→2MgO(s)+energy
the remaining mg reacts with the water and co2 produced
Mg(s)+2H2O→Mg(OH)2(s)+H2(g)
Mg(s)+CO2→2MgO(s)+C(s)

The reason why it gets hot is that there is a COMBUSTION reaction such the Mg metal plus oxygen makesMgO called magnesium oxide