What is metaphophoric (HPO3)?

Polymeric form of Ortho phosphoric is called meta phosphoric acid, it exist as dimer, trimer and polymer but trimer and Hexamer is more common.

(1) Trimer of phosphoric acid exists as cyclic trimer which contains three P-O-P bonds.

(2) Hexamer of phosphoric acid exist as sodium salt which is called sodium metaphophate or sodium polymetaphosphate and it is commercially  known as "CALGON" and use as water softener.

Related Questions:

What are "pyro" oxy acids?

What are "Ortho" or "Meta" oxyacids?

What is Meta Boric Acids?

What are the structural difference between oxides ( P4O6 and P4O10) of phosphorous?

What are common structural features of oxides (P4O6 and P4O5) of phosphorous?

Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

 In Borazine molecule, nitrogen is more electro negative than the boron. Nitrogen acquires partial negative charge and boron acquires partial positive charge and back bonding take place between boron and nitrogen. And it is more reactive as compared with Benzene, because Borazol is less stable and more reactive toward Electrophilic Aromatic Substitution reactions due to high polarity of B-N bonds borazine molecule while in benzene all bonds are non polar.

                                 Borazine