Question

The number of P=O and P-O-P bonds present in the oxoacid of phosphorus, prepared by treating red P$_4$ with alkali, are respectively

• A. 2, 1
• B. 1, 1
• C. 1, 2
• D. 2, 2

Hint:

For phosphorus oxoacids from P$_4$ reactions, identify the product (e.g., H$_4$P$_2$O$_6$ from red P$_4$ + alkali) and count P=O (double bonds) and P-O-P (P-O-P linkages) in its structure.

Answer 1

The Correct Option is A

When red phosphorus (P$_4$) reacts with alkali (e.g., NaOH) in the presence of water, it undergoes disproportionation to form hypophosphoric acid (H$_4$P$_2$O$_6$) and phosphine (PH$_3$). The reaction is: \[ \text{P}_4 + 4\text{NaOH} + 4\text{H}_2\text{O} \rightarrow 2\text{H}_4\text{P}_2\text{O}_6 + 2\text{PH}_3 \] Hypophosphoric acid has the structural formula: \[ \chemfig{HO-P(=O)(-OH)-O-P(=O)(-OH)-OH} \] Analyze the structure: P=O bonds: Each phosphorus atom is bonded to one oxygen atom via a double bond. There are two phosphorus atoms, so there are two P=O bonds (one per P).
P-O-P bonds: The two phosphorus atoms are connected through a single oxygen atom, forming one P-O-P linkage.
Thus, the number of P=O bonds is 2, and the number of P-O-P bonds is 1. Option (1) is correct. Options (2), (3), and (4) do not match the structure of H$_4$P$_2$O$_6$.