Question

how do the differences in the polyatomic ions po3^3- and po4^3- help you determine whether each ends in -ite or -ate

Answer 1

Explanation:

PO3^3- ==> The Phosphite anion

PO4^3 ==> The phosphate anion

Upon observation of both anions, what seems to be the differences?

Two can be spot.

The number of oxygen present and the oxidation number of phosphorus.

The difference in suffixes however is caused by the number of oxygen present.

Generally, in chemical nomenclature; -ate posseses more oxygen and =ite possess less oxygen.

A typical example is Nitrate and nitrite;

Nitrate ==> NO3-

Nitrite ==> NO2-

Answer 2

The suffixes -ite and -ate depends on which polyatomic ion has more oxygen atoms.
-ite (less oxygen) 
-ate (more oxygen)