Which one of the following is based on the heating effect of current 1. Geyser
2. Hair dryer
3. Immersion rod
4. All of these

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.

I’m not sure about this question

They cool it down and aluminum cools easily