Metaphosphoric acid is:

The correct answer is Option (3) → \((HPO_3)_3\)

Metaphosphoric acid has the empirical formula \( \ce{HPO3} \) and exists only in polymeric forms, (HPO₃)_n, with phosphorus in the +5 state. Its cyclic trimer, cyclotrimetaphosphoric acid, (HPO₃)₃, is a ring of three \( \ce{PO4} \) units joined through P–O–P bonds, each P carrying one –OH and one P=O.

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