Question

Which of the following oxoacids of phosphorus is a reducing agent and a monobasic acid as well
A.${{\text{H}}_{\text{4}}}{{\text{P}}_{\text{2}}}{{\text{O}}_{\text{5}}}$
B.${\text{HP}}{{\text{O}}_{\text{3}}}$
C.${{\text{H}}_3}{\text{P}}{{\text{O}}_{\text{3}}}$
D.${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{2}}}$

Answer 1

Hint: Oxoacids: They are also known as oxyacids. It is defined as the acid which contains oxygen or we can say those acids in which one element is oxygen and contains at least one oxygen linked to hydrogen.

Complete step by step solution:
First of all let us talk about oxoacids.
Oxoacids: They are also known as oxyacids. It is defined as the acid which contains oxygen or we can say those acids in which one element is oxygen and contains at least one oxygen linked to hydrogen.
Oxoacids of phosphorus: In oxoacids of phosphorus the oxygen-phosphorus double bond is present and oxygen with hydrogen bond is present along with these two groups phosphorus-phosphorus and phosphorus-hydrogen bonds are also present.
Mono-Basic acid: It is defined as the base which is neutralized by one mole of acid.
Di-basic acid: It is defined as the base which is neutralized by two moles of acid.
In oxoacids of phosphorus the hydrogen which is attached to oxygen can contribute to the basic character of the molecule.
${{\text{H}}_{\text{4}}}{{\text{P}}_{\text{2}}}{{\text{O}}_{\text{5}}}$: This is an oxoacid of phosphorus which is known as pyrophosphoric acid. In this molecule two hydrogen-oxygen bonds are there, two oxygen-phosphorus double bonds, one phosphorus-oxygen-phosphorus bond and two phosphorus-hydrogen bonds. It is dibasic acid.
${\text{HP}}{{\text{O}}_{\text{3}}}$: This is an oxoacid of phosphorus which is known as metaphosphoric acid. In this molecule one hydrogen-oxygen bond is there, two oxygen-phosphorus double bonds. So it is monobasic acid.
${{\text{H}}_3}{\text{P}}{{\text{O}}_{\text{3}}}$: This is an oxoacid of phosphorus which is known as phosphoric acid. In this molecule two hydrogen-oxygen bonds are there, one oxygen-phosphorus double bond and one phosphorus-hydrogen bond. So it is dibasic acid.
${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{2}}}$: This is an oxoacid of phosphorus which is known as hypophosphoric acid. In this molecule one hydrogen-oxygen bond is there, one oxygen-phosphorus double bond and two phosphorus-hydrogen bonds. So it is monobasic acid.
Reducing agent: These are those substances which can reduce others and get oxidized themselves. Here metaphosphoric acid does not act as a reducing agent because there is no hydrogen in the molecule. So the oxoacid of phosphorus which is a reducing agent and a monobasic acid as well is hypophosphoric acid.

Hence option D is correct.

Note: Oxidising agents : These are those substances which oxidise (addition of oxygen or removal of hydrogen) others and reduced (addition of hydrogen or removal of oxygen) themselves, are known as oxidizing agents.