For the ion PO₄³−, what are the formal charges on each oxygen atom and the bond order of the P-O bond, respectively?
a) Formal charge: -2 on each oxygen; Bond order: 1
b) Formal charge: 0 on each oxygen; Bond order: 2
c) Formal charge: -1 on each oxygen; Bond order: 1.5
d) Formal charge: -1 on each oxygen; Bond order: 2