Which chemical equation is correctly balanced? . 1) na + o2  na2o . 2) na + o2  2 na2o. 3) 2 na + 2 o2  2 na2o. 4) 4 na + o2  2 na2o.

"4 Na + O2  2 Na2O" is the one chemical equation among the following choices given in the question that is correctly balanced. The correct option among all the options that are given in the question is the fourth option or option "4". I hope that this is the answer that has actually come to your great help.

They can measure  the amount of energy gained or lost