The correct option is: (a) -0.75,1.25
Explanation:
The total charge = -3
So the average formal charge on each 'O' atom is = 3/4 = -0.75
Again total no. of electrons in the valence shell of PO43- ion = 5 + 8 = 13
No. of electrons involved in bond formation in PO43- ion = 13 - 3 = 10
No. of bonds in PO43- = 10/2 = 5
=> Average P - O bond order = 5/4 = 1.25