Question

for the phosphoric acid molecule (h₃po₄), all four oxygen atoms are bonded to the central phosphorus atom and the three hydrogen atoms are bonded to different oxygen atoms. several resonance structures can be drawn for h₃po₄ but one structure is more important than the others.
in the most important structure, the phosphorus atom has:
a formal charge of zero and an expanded octet
a formal charge of +1 and a complete octet
a formal charge of zero and a complete octet
a formal charge of +5 and an expanded octet
a formal charge of -1 and an expanded octet

Explanation:

Step1: Calculate formal charge

Formal charge formula: \(FC = V - N - \frac{B}{2}\), where \(V\) is valence electrons (\(V = 5\) for \(P\)), \(N\) is non - bonding electrons (\(N = 0\) in the most important resonance structure), \(B\) is bonding electrons (\(B = 8\)).
\(FC=5 - 0-\frac{8}{2}=5 - 4 = 1\) (incorrect, let's check another way).
In the most stable resonance structure of \(H_3PO_4\), \(P\) has 5 bonds (3 single bonds to \( - OH\) groups and 1 double bond to \(O\)). Valence electrons of \(P\) is 5. Non - bonding electrons \(N = 0\). Bonding electrons \(B = 10\). \(FC = 5-0-\frac{10}{2}=0\).

Step2: Check octet rule

\(P\) is in the third period. It can have an expanded octet. In \(H_3PO_4\), \(P\) has 10 electrons (5 pairs) around it (expanded octet).

Answer:

a formal charge of zero and an expanded octet