Question

How many resonance structures can be drawn for $\text{PO}_{\text{4}}^{\text{3}-}$-?

Answer 1

Resonance structures are sets of lewis structures that describe the delocalization of electrons in a polyatomic ion or a molecule. They describe chemical bonding of a molecule or polyatomic ion.

Complete step by step answer:
When we draw resonance structures, we convert ion pairs to bonds and bonds to ione paris.
Resonance structures of any molecule can be drawn from the lewis structure of that molecule. Lewis structure of phosphate ion $\text{(PO}_{\text{4}}^{\text{3-}}\text{)}$

In Lewis structure of $\text{PO}_{\text{4}}^{\text{3}-}$ ion, there are three lone pairs in three oxygen atoms and other oxygen atom that is connected to phosphorus atom has two lone pairs and double bond.
Let's draw four stable resonance structures for the phosphate ion.

These are the four resonance structure of $\text{PO}_{4}^{3-}$

Note: From the above it is clear that, higher the resonance structure higher will be the stability of the molecule or ion. From various resonating structures, resonance hybrids will form. The contribution of resonating structure depends upon the stability of the resonating structure. The energy of resonating structures is higher than the energy of resonance hybrids. The resonance hybrid is the structure which is the most stable structure.