What is the correct way to write the chemical symbol for sodium?
The chemical symbol of sodium is Na.
Na is the symbol for sodium.
Draw the symbol for Sodium and Chlorine. This would create sodium chloride, which is table salt. The symbol for sodium is Na, so you write this down. Beside it, you write the symbol for Chlorine, which is Cl, then you place this in square brackets. After doing so, you may now place it's ionic charge outside the brackets in subscript. The result would be Na[Cl]-1.
IUPAC (International Union for Pure and Applied Chemistry) has rules for writing chemical symbols and formulas. They are valid in all languages. For compounds search in a library Nomenclature of inorganic compounds and Nomenclature of organic compounds, with the text adapted to your language, if necessary. See the links below.
How would one write out liquid water water vapor aqueous sodium chloride and solid sodium chloride in chemical equations?
Elemental sodium actually exists as a metallically bonded solid. It is customary to write the formula of solid sodium as "Na". It would not be correct to write "Na2", because in a metallically bonded solid every atom is equally strongly bonded to each of its several nearest neighbors, always more than 2, in the crystal lattice.