Question

what are ionizable ions?

Answer 1

any uncharged group in a molecular entity that is capable of dissociating by yielding an ion (usually an H+ ion) or an electron and itself becoming oppositely charged, or ... From: ionizable group in Oxford Dictionary of Biochemistry and Molecular Biology » 

Answer 2

hello friend..

when an electron itself becomes oppositely charged to form ionizable group then know as Ionizable Ion.

hope it will help you.
best wishes.