Identify the form of phosphoric acid with the empirical formula HPO3: which named type of phosphoric acid corresponds to HPO3?

Introduction / Context:
Phosphoric acids appear in several condensation states depending on the degree of dehydration: orthophosphoric (H3PO4), pyrophosphoric (H4P2O7), and metaphosphoric (general formula (HPO3)n). Correctly mapping molecular formulas to these named forms is essential in fertilizer chemistry and inorganic nomenclature.

Given Data / Assumptions:

• HPO3 is provided as the empirical unit.
• We are to choose the named acid family that corresponds to this unit.
• No polymerization degree n is specified, so we refer to the repeating unit.

Concept / Approach:
Metaphosphoric acid is represented by (HPO3)n, where n can be 1 (monomeric metaphosphoric) or greater (polymeric ring or chain structures). Orthophosphoric acid is H3PO4, and pyrophosphoric acid is H4P2O7, both inconsistent with HPO3. Therefore, HPO3 maps directly to the metaphosphoric family.

Step-by-Step Solution:
Compare given formula HPO3 with standard acids.Orthophosphoric: H3PO4 → not equal.Pyrophosphoric: H4P2O7 → not equal to a single HPO3 unit.Metaphosphoric: (HPO3)n → matches the given empirical unit.

Verification / Alternative check:
Chemical handbooks list metaphosphoric acid as derived by dehydration of orthophosphoric acid, yielding the HPO3 repeating unit; polyphosphates and metaphosphates are widely used in industry.

Why Other Options Are Wrong:
Pyro- and ortho- formulations have different stoichiometries and hydrogen/oxygen counts.“None of these” is incorrect because metaphosphoric exactly matches.

Common Pitfalls:
Confusing empirical and molecular formulas or forgetting that metaphosphoric can polymerize (n > 1).

Final Answer:
Metaphosphoric acid