* Ionic Compounds are formed by the electrostatic attraction between oppositely charged ions.

* Sodium (Na) is a metal and forms a positively charged ion (Na+).

* The phosphate group (PO4)3- is a polyatomic ion with a negative charge.

* Sodium tripolyphosphate consists of a combination of these ions. The tripolyphosphate anion (P3O10)5- is formed by the linking of three phosphate groups.

Therefore, the attraction between the positively charged sodium ions and the negatively charged tripolyphosphate ions holds the compound together, making it an ionic compound.