Answer: d. 4Na + O₂ → 2Na₂O
Step-by-step explanation:
Balancing a chemical equation means making sure that there are equal numbers of each type of atom on both the left and right sides of the equation. In option (d), there are 4 sodium (Na) atoms and 2 oxygen (O) atoms on both sides of the equation, so it is balanced.
Options (a), (b), and (c) do not have equal numbers of each type of atom on both sides, so they are not balanced.