Phosphoric acid ($H_3PO_3 $)
Phosphoric acid, with the chemical formula $H_3PO_3 $, has unique characteristics in the field of chemistry. Its properties are quite specific, showing medium and strong acidity, which is stronger than that of phosphoric acid. This is because in the phosphoric acid structure, although there are three hydrogen atoms, only two hydroxyl hydrogens can be ionized. Unlike the ternary acid of phosphoric acid, phosphoric acid is a dibasic acid.

In terms of its characteristics, pure phosphoric acid is colorless crystalline, deliquescent, and highly soluble in water. This is because its molecules and water molecules can form hydrogen bonds, so it is very soluble. Its melting point is about 74 dollars ^ {\ circ} C $, and it is easily decomposed when heated to form phosphoric acid and phosphine and other substances.

Phosphoric acid has a wide range of uses. In the agricultural field, it is often used as a raw material for fungicides. Because of its certain reducing properties, it can interfere with the metabolic process of pathogens, inhibit the growth of pathogens, and protect crops from disease infestation. In the chemical industry, it is an important reducing agent. In organic synthesis reactions, certain oxygen-containing compounds can be reduced, such as nitro compounds to amine compounds. This reduction process has relatively mild conditions and good selectivity. It is an important means of organic synthesis.

As for the reaction, phosphoric acid can neutralize with bases. If it reacts with sodium hydroxide, depending on the amount of base, disodium hydrogen phosphite ($Na_2HPO_3 $) or sodium dihydrogen phosphite ($NaH_2PO_3 $) can be generated. It can also react with active metals to produce hydrogen. If it reacts with zinc, the chemical equation is: $Zn + H_3PO_3 = ZnHPO_3 + H_2 ↑ $. And phosphorus can be oxidized to phosphoric acid by strong oxidants. If it reacts with hydrogen peroxide, hydrogen peroxide oxidizes the phosphorus element in phosphorus from $+ 3 $to $+ 5 $to form phosphoric acid.

In short, phosphorus with its unique properties plays an important role in many fields and occupies an indispensable position in chemical research and industrial production.