Answer the question on the basis of the passage given below:
Oxides formed by \(p\)- block elements are acidic, basic and neutral. Also, elements of \(p\)-block form different acids.
In a cyclotrimetaphosphoric acid molecule, how many single and double bonds are present?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 3 - double bonds, 12 - single bonds
In the oxoacids of phosphorus, each phosphorus atom is tetrahedral: it has one P=O bond and at least one P–OH bond. Metaphosphoric acid has the formula \( \ce{HPO3} \); cyclotrimetaphosphoric acid, \( \ce{(HPO3)3} \), is a six-membered ring of three P atoms joined by three bridging O atoms (P–O–P).
Counting the bonds in \( \ce{(HPO3)3} \):
P=O: one on each P → 3 double bonds
P–O in the ring: each of the 3 bridging O atoms has two P–O bonds → 6 single bonds
P–OH: one on each P → 3 P–O single bonds and 3 O–H single bonds → 6 single bonds
\( \text{single bonds} = 6 + 3 + 3 = 12 \)
So the molecule has 3 double bonds and 12 single bonds.
Shortcut: every P in an oxoacid of phosphorus has one P=O, so three P atoms give 3 double bonds; only Options (1) and (3) have 3, and Option (3) leaves out the three O–H bonds (6 + 3 = 9).
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Oxoacids of Phosphorus – …
