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Q.
In $ PO_{4}^{3-} $ ion, the formal charge on each oxygen atom and $P-O$ bond order respectively are :
AIPMTAIPMT 1998Chemical Bonding and Molecular Structure
Solution:
$P - O$ bond order
$=\frac{\text { Number of bonds in all possible direction between two atoms }}{\text { Total number of resonating structures }}$
Average formal charge on each of the oxygen atom in calculated as follows:
(i) Total number of electrons present in valence shell of
$P - O =5+8=13$
(ii) Number of electron involved in bond formation
$=13-3$
$=\frac{5}{4}=1.25$
$=\frac{2+1+1+1}{4} $
$=\frac{5}{4}$
Resonating structures are
Total charge on $PO _{4}^{3-}$ ion is $-3$
$=\frac{\text { Total charge }}{\text { Total entity of } O \text {-atom }}$
So, the average formal charge on each O-atom is
$=-\frac{3}{4}=-0.75$
