First write out the equation given:Na + O2 —> Na2ONow count how many oxygen atoms are on the LHS of equation (2) and how many are on the RHS (1). This means you must put a 2 in front of the Na2O to BALANCE the oxygens:Na + O2 —> 2 Na2ONow count how many sodium atoms are in the LHS of equation (1) and how many are on the RHS (4). This means you must put a 4 in front of the Na to BALANCE the sodium’s:4Na + O2 —> 2Na2O