Question

Which of the following is a tetrabasic acid?

• A. Hypophosphorous acid
• B. Metaphosphoric acid
• C. Pyrophosphoric acid
• D. Orthophosphoric acid

Answer 1

The correct option is C

Pyrophosphoric acid

Explanation for correct option:

C. Pyrophosphoric acid

• Pyrophosphoric acid is a diphosphoric acid with a chemical formula ${\mathrm{H}}_4{\mathrm{P}}_2{\mathrm{O}}_7$.
• It is soluble in water/ ethyl alcohol as well as diethyl ether.
• This acid contains four replaceable hydrogens thus it is a tetrabasic acid.
• The structure of Pyrophosphoric acid is given below:

Explanation for incorrect options:

A. Hypophosphorous acid has a chemical formula ${\mathrm{H}}_3{\mathrm{PO}}_2$ and it is a dibasic acid due to the presence of two replaceable hydrogens.

B. Metaphosphoric acid has a chemical formula ${\mathrm{HPO}}_3$ and it is a monobasic compound as it has only one replaceable hydrogen.

D. Orthophosphoric acid has a chemical formula ${\mathrm{H}}_3{\mathrm{PO}}_4$ and it is a tribasic acid due to the presence of three replaceable hydrogens.

Hence, the correct option is C i.e. Pyrophosphoric acid.