Ionization of hydrogens in hypophosphorous acid Does anyone know why the hydrogen atoms bonded with phosphorus in $\ce{H3PO2}$ are not ionizable? 

I tried looking in high school level books, but they only describe the process, not the real reason. I would appreciate if someone has the answer.
To begin with, removing another proton from anionic species is not very favorable. For example, the monohydrogen phosphate dianion is not very acidic $(\mathrm{p}K_\mathrm{a}\sim 12)$ despite it having an $\ce{OH}$ group.

In the case of $\ce{H3PO2},$ the second and third protons are bonded directly to $\ce{P},$ which is much less electronegative than $\ce{O},$ and consequently these P-H bonds are much less polarized than an $\ce{O-H}$ bond. So these protons are unable to ionize appreciably in aqueous solution.