Question

In PO₄³-, the formal charge on each oxygen atom and the P–O bond order respectively are:

• A. \(-0.75,\;0.6\)
• B. \(-0.75,\;1.0\)
• C. \(-0.75,\;1.25\)
• D. -3,1.25

Hint:

For resonance-stabilized ions: • Bond order = (sum of bond orders)/(number of bonds) • Formal charge is averaged over equivalent atoms

Answer 1

The Correct Option is C

Step 1: The phosphate ion PO₄³- has four equivalent resonance structures. In each structure, there is: • one P=O double bond • three P-O⁻ single bonds
Step 2: Total bond order of all P–O bonds: 2 + 1 + 1 + 1 = 5
Step 3: Average P–O bond order: Bond order = (5)/(4) = 1.25
Step 4: Total negative charge on oxygen atoms is -3, shared equally among 4 oxygen atoms: Formal charge on each O = (-3)/(4) = -0.75