find bond order and formal charge of SO₄-2 and PO₄ ^-3

Draw the resonance structures for SO4 ^2-

between any two atoms : overall bond order = bond order in each resonance structure / no. of such structures

concentrate on one single S-O bond. There is total 9 bonds on any of S-O with in 6 structures.

so the bond order is = 9/6 = 1.5

formal charge can be calculated as:No. of  valence electrons - No.of non bonding electrons - (1/2) of bonding electrons.

For Sulfur : 6-0-12/2= 0

similarly you can calculate any of Oxygen

For PO4^3- draw the resonance structure

Bond order = 6/5 = 1.2

formal charge on P = 5 - 0-10/2 = 0

similarly you can calculate for any of oxygen.