Solution:
Higher order ionization constants are smaller than the lower order ionization constans() of a polyprotic acid. The reason for this is that it is more difficult to remove a positively charged proton from a negative ion due to electrostatic forces.
This can be seen in the case of removing a proton from the uncharged as compared from a negatively charged .
Similarly, it is more difficult to remove a proton from a doubly charged anion as compared to .