Question

Define the term 'basicity' of an acid. Give the basicity of: nitric acid, sulphuric acid and phosphoric acid.

Answer 1

Hint:‌To solve this question, we must first understand the whole concept of Basicity and the method of calculation of basicity. Then we need to assess and use the procedure to find the basicity of the required compounds and then only we can conclude the correct answer.

Complete step by step answer:
Before we move forward with the solution of this given question, let us first understand some basic concepts:
Basicity: the basicity of a molecule is a measure of its ability to accept a proton $(H^{+})$ to form a stable product. If the product is a cation, then anything that stabilizes the positive charge will increase the strength of the base.
The Basicity of an acid is defined as the number of replaceable hydrogen atoms of that particular acid by a base. This should not be misinterpreted as the number of hydrogen atoms in that acid. For example, Hypophosphorous Acid $H_{3}P{O}_2$ has $3$ hydrogen atoms but only one replaceable hydrogen. Thus it is monobasic.
We must be aware that replaceable hydrogen atoms are the ones that are bonded with the oxygen atoms and not the ones that are bonded to the central metal atom. The ones that are directly bonded play a reducing character.
The required basicity of the compounds according to the above mentioned concept of replaceable H atoms are:
Nitric acid: Basicity $=1$
Sulphuric acid : Basicity $=2$
Phosphoric acid : Basicity $=3$

Note: The convenient way to look at basicity is based on electron pair availability the more available the electrons, the more readily they can be donated to form a new bond to the proton and, and therefore the stronger base.