What is meant by the basicity of an acid ?

Solution:
Basicity of an acid is defined as its ability to donate H⁺ in an aqueous solution.
For example, the basicity of H₂SO₄ is 2 since H₂SO₄ $\underset{}{\to }$ 2H⁺ + SO₄^2-
                      The basicity of HNO₃ is 1 since HNO₃ $\underset{}{\to }$ H⁺ + NO₃​​​​​^-