Which of the compounds h2c2o4, ca(oh2, koh, and hi, behave as bases when they are dissolved in water?

H2C2O4, also written as (COOH)2, is Ethandioic acid, and, as evident by the name, is an acid, and not a base
Ca(OH)2 and KOH, Calcium Hydroxide and Potassium Hydroxide, respectively, are bases when dissolved in water, as they are able to release OH- ions.
Hydrogen Iodide, HI, when dissolved in water, is a strong acid. So, that is also not a base.

You would be correct, boiling water does disinfect contamination.    the property of disinfecting means to kill  germs, bacteria and other pathogens or contamination  that might cause an infection or cause a person to become sickly. a couple methods of disinfecting are using soap, other cleaning supplies or by simply "boiling" the contaminate.  the reason why boiling water disinfects certain attributes is because some cells cannot survive the heat and pressure.