Question

An acid with molecular formula ${C_7}{H_6}{O_3}$ forms three types of sodium salts, which
are: \[{C_7}{H_5}{O_3}Na,{C_7}{H_4}{O_3}N{a_2}{\text{ and
}}{{\text{C}}_{\text{7}}}{{\text{H}}_3}{{\text{O}}_{\text{3}}}{\text{N}}{{\text{a}}_{\text{3}}}\]
The basicity of this acid is:

Answer 1

Hint:Acidity and basicity are concepts of denoting the replaceable ions. Acidity is how many acid molecules can be neutralised by 1 molecule of base, or replaceable \[O{H^ - }\] ions. While basicity is how many base molecules can be neutralised by 1 molecule of acid, or replaceable \[{H^ + }\] ions.

Complete step by step answer:
We know the definition of basicity is the number of replaceable \[{H^ + }\] ions from the acid. In other
words, the ionisable \[{H^ + }\] ions from acid to form salts when reacts with base.
Acid and bases react to form salt and water, this is called neutralisation reaction.
\[{\text{Acid + Base }} \to {\text{ Salt + Water}}\]
Now, here the replaceable ions from acid and base will only react and that number of replaceable ions
will be the acidity of base and basicity of acids.
Here in above question, we have been given acid having 6 hydrogen atoms with formula of
${C_7}{H_6}{O_3}$ , it is not necessary that all 6 hydrogen can be replaced, but the replaceable hydrogen
atoms will come out and salt will be obtained.
Again in above question, we have been given 3 salts formed from this acid which have formula of
\[{C_7}{H_5}{O_3}Na,{C_7}{H_4}{O_3}N{a_2}{\text{ and
}}{{\text{C}}_{\text{7}}}{{\text{H}}_3}{{\text{O}}_{\text{3}}}{\text{N}}{{\text{a}}_{\text{3}}}\] , now we
can see that in first salt 1 hydrogen is replaced by 1 sodium atom, while in second 2 hydrogen replaced by
2 sodium atoms, and at last 3 hydrogen are replaced by 3 sodium atoms to get salts. This implies that
maximum 3 hydrogen atoms can be replaced and ionized from acid.
Thus, the basicity of the above acid is 3.

Additional information: The classical definition of acids and bases can be defined as follows:
Acid: those molecules which give \[{H^ + }\] ions in aqueous solution.
Bases: those molecules which give \[O{H^ - }\] ions in aqueous solution.

Note:
One may be mistaken to write basicity to be total number of hydrogen in acid, but we should know
that only ionisable or replaceable hydrogen, \[{H^ + }\] ions will give us basicity.
In reaction to acid and base, salt is formed. If acid and base are not strong then step by step reaction
takes place, and one by one hydrogen gets replaced by metal ions to form salts from acid. As seen in this
question, 3 types of salt are formed, by replacement of hydrogen one by one.