What is a polyprotic acid? Give examples of polyprotic acids and explain their ionization.

Polyprotic acid: Acids that have more than one ionizable proton per molecule. These are also known as polybasic acids.
Diprotic acid: An acid that has two ionizable protons per molecule. These are also known as dibasic acids.
General ionization for a diprotic acid $(H_2X)$:
$H_2X_{(aq)} \rightleftharpoons 2H^+_{(aq)} + X^{2-}_{(aq)}$
The ionization occurs in two steps:
$(i) H_2X + H_2O \rightleftharpoons H_3O^+ + HX^- \quad K_{a1}$
$(ii) HX^- + H_2O \rightleftharpoons H_3O^+ + X^{2-} \quad K_{a2}$
Here,$K_{a1} > K_{a2}$ and the overall dissociation constant $K_a = K_{a1} \times K_{a2}$.
Examples of diprotic acids: Oxalic acid $(H_2C_2O_4)$,Sulphuric acid $(H_2SO_4)$,Carbonic acid $(H_2CO_3)$,and Sulphurous acid $(H_2SO_3)$.
Examples of triprotic acids: Phosphoric acid $(H_3PO_4)$ and Citric acid.
In a polyprotic acid solution,a mixture of various acid species like $H_2A$,$HA^-$,and $A^{2-}$ exists in equilibrium.