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Phosphorus forms two series of oxyacids namely; phosphorus acid and phosphoric acid.

SN	Element	Formula	Name of the Oxyacid	O.S.
2	Phosphorus	H₃PO₂ H₃PO₃ H₄P₂O₇	Hypo Phosphorus acid Ortho Phosphorus acid Pyro phosphorous acid	+1 +3 +3
3	Phosphoric	H₄P₂O₆ H₃PO₄ H₄P₂O₇ (HPO₄)_n	Hypo Phosphoric acid Ortho Phosphoric acid Pyro Phosphoric acid Meta phosphoric acid	+4 +5 +5 +5
4	Arsenic	H₃AsO₃ H₃AsO₄	Arsenious acid Arsenic acid	+3 +5
5	Sb & Bi	No stable acid

(A) Phosphorus acid series: (Structure)

The series consists of p atom exhibiting oxidation state of +3. They act as reducing agents.

(B) Phosphoric acid series: (Structure)

This series consist of acids having p in +5 oxidation state.

Note : Meta phosphoric does not exist in monomeric form, but it exists as cyclo meta phosphoric acid (HPO₃)₃ or polymeta phosphoric acid (HPO₃)_n. Sodiumhexametaphosphate is a famous salt known as CALGON and use water softener.

Special Note:

(1) Meta is used for acid obtained by loss of H₂O molecule.

(2) Pyro is used for the acid obtained from two molecules with a loss of H₂O.

(3) Hypo is used for the acid having lower oxygen content than the parent acid.

Related Questions:

Which is more basic N(CH3)3 or N(SiH3)3 , explain?

Are all the five bonds of PCl5 equivalent? Justify your answer.

Trisilyl amine, N(SiH3)3 is planar whereas trimethyl amines N(CH3)3 is pyramidal. Explain why?.

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

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

What are abnormal behaviour of Nitrogen atom as compared to other family members?

What is product obtained when N2O5 is treated with NaCl?

What is metaphophoric (HPO3)?

Phosphorus can form PCl5 but nitrogen can not form NCl5 why?

Why PCl3 hydrolysed while NCl3 can not be hydrolysed?

Why bond angle of hydrides of group 15, decreases down the group?

What is "calgon" ? Give structure and its uses?

Why nitrogen shows catenation properties less than phosphorus?

Why Nitrogen is fairly inert gas?

Why Nitrogen (N2) is less reactive at room temperature?

Why Nitrogen dioxide (NO2) dimerises to form Dinitrogen tetraoxide (N2O4)?

Why Nitrogen dioxide (NO2) is coloured but Dinitrogen tetraoxide (N2O4) is colourless?

Hypophosphorous acid (H3PO2) and Phosphorous acid (H3PO3) act as as good reducing agents while H3PO4 does not.Why?

S.N.	Formula	Name of acids	Oxidation No. of N
1	H₂N₂O₂ or HNO	Hyponitrous acid	+1
2	H₄N₂O₄ or H₂NO₂	Hydroxynitrous acid	+2
3	HONO or HNO₂	Nitrous acid	+3
4	HOONO	Pernitrous acid	+4
5	HNO3	Nitric acid	+5
6	HNO4	Pernitric acid	+6

(1) Hyponitrous acid (H₂N₂O₂):

Hyponitrous acid is a chemical compound with formula H₂N₂O₂ or HON=NOH. Hyponitrous acid is a weak acid in aqueous solution and decomposes to N₂O and water. It is an isomer of nitramide [H₂N−NO₂].

Hyponitrous acid forms two series of salts, the hyponitrites containing the [ON=NO]²⁻ anion, and the "acid hyponitrites" containing the [HON=NO]⁻anion.

(2) Nitrous acid (HNO₂):

Nitrous acid (HNO₂) is a weak and monobasic acid known only in solution and in the form of nitrite (NO₂⁻) salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes.