Balance each of the following chemical equations:
a. N2(g) + O2(g) → NO(g)
b. HgO(s) = Hg(l) + O2(8)
c. Fe(s) + O2(g) →→ Fe2O3(s)
d. Na(s) + Cl2(g) →→ NaCl(s)
e. Cu2O(s) + O2(g)
→ CuO(s)