Effective charge = charge / no. of oxygen atoms = 3/4 = -0.75 there are only 3negative charges distributed on 4 oxygen atoms therefore 3/4.......hope you got it

Effective Charge on Each Oxygen Atom:
The PO4^3- ion consists of one phosphorus atom and four oxygen atoms. Each oxygen atom has a formal charge of -2. In the PO4^3- ion, the oxygen atoms share their electrons with the phosphorus atom, resulting in a negative charge on each oxygen atom.

To calculate the effective charge on each oxygen atom, we need to consider the formal charge and the electron density around the oxygen atom. The formal charge is the difference between the valence electrons of an atom and its lone pairs and the number of bonds it forms. In the case of oxygen in the PO4^3- ion, it has 6 valence electrons and forms three single bonds with the phosphorus atom.

Formal Charge Calculation:
Valence electrons of oxygen = 6
Lone pairs of oxygen = 6 - 3 (bonds) = 3
Formal charge = valence electrons - lone pairs - 1/2(bonds)

For each oxygen atom in the PO4^3- ion:
Formal charge = 6 - 3 - 1/2(3) = 0

Therefore, the formal charge on each oxygen atom is 0. This indicates that each oxygen atom in the PO4^3- ion is not fully charged.

P-O Bond Order:
The bond order represents the number of bonds between two atoms in a molecule or ion. In the case of the PO4^3- ion, there are four P-O bonds.

To calculate the bond order between phosphorus and oxygen, we need to consider the number of bonding electrons and the number of antibonding electrons.

In the PO4^3- ion, there are a total of 32 valence electrons:
Phosphorus contributes 5 valence electrons, and each oxygen contributes 6 valence electrons (4 oxygens x 6 electrons).

The Lewis structure of the PO4^3- ion shows that each oxygen atom forms a single bond with the phosphorus atom, resulting in four P-O bonds.

Bond Order Calculation:
Bond order = (number of bonding electrons - number of antibonding electrons) / 2

In each P-O bond:
Number of bonding electrons = 2
Number of antibonding electrons = 0

Bond order = (2 - 0) / 2 = 1

Therefore, the bond order between phosphorus and oxygen in the PO4^3- ion is 1. This indicates a single bond between phosphorus and each oxygen atom.

Summary:
The effective charge on each oxygen atom in the PO4^3- ion is 0, indicating that the oxygen atoms are not fully charged. The P-O bond order is 1, indicating a single bond between phosphorus and each oxygen atom.

Based on these calculations, the correct answer is (3) -0.75, 0.6.