Answer:
2Mg(s) + O2(g) -> 2MgO(s)
Step-by-step explanation:
Mg(s) + O2(g) -> MgO(s)
1 Mg atom and 2 O atoms on the reactant side | 1 Mg atom and 1 O atom on the product side.
add a 2 infront of MgO to balance the O atoms:
Mg(s) + O2(g) -> 2MgO(s)
Now there's 1 Mg atom and 2 O atoms on the reactant side | 2 Mg atoms and 2O atons on the product side.
Now add a 2 infront of the Mg on the ractant side:
2Mg(s) + O2(g) -> 2MgO(s)
Now there are 2 Mg and 2 O atoms on both the reactant and product sides.