Write the formula for sodium phosphate.

Hint: At the earliest stage chemical formulas are obtained of any molecule by determining the masses of all the elements that are combined to form a molecule after that two important types of formulas in chemistry are comes which are known as molecular formula and empirical formula.

Complete answer:
Sodium phosphate is defined as the generic term for a variety of salts of sodium represented by the chemical formula $N{{a}^{+}}$ and phosphate represented by the chemical formula $P{{O}_{4}}^{3-}$. In this molecule cation i.e. positively charged ions and anions i.e. negatively charged anions are present. Mostly salt of this category found to be stable both in aqueous as well as non-hydrated form. The hydrates are most common as compared to non-hydrated forms.
Sodium phosphate is generally made up of two substances called sodium ions and phosphate ions the formula for sodium phosphate can be written as $N{{a}_{3}}P{{O}_{4}}$. There are three families of sodium phosphate are generally known which are derived from ortho phosphate, hydrogen phosphate and dihydrogen phosphate represented by the formulas $P{{O}_{4}}^{3-},\ \text{H}P{{O}_{4}}^{2-}and\ {{H}_{2}}P{{O}_{4}}^{-}$ respectively. Rather than this there is also di and polyphosphates form are also present which forms a number of useful salts with other polymers.
Hence from the above discussion we conclude that the formula for sodium phosphate is $N{{a}_{3}}P{{O}_{4}}$.

Note:
Sodium phosphates have many applications in food and for water treatment. Like sodium phosphates are often used as emulsifiers and leavening agents for bakery items it is also used to control pH of processed foods and can also be used in medicine for constipation.