If you drop a ice cube in a glass of lemonade, what makes the lemonade cold?

The ice cube's cold water as it melts into the lemonade makes it cold.
The way this happens is the ice steals the relitive warmth from the lemonade, causing itself to melt, which lets out its (still cold) water into the lemonade.

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.