Which atom would be neutral? 1an oxygen atom with 16 electrons, 18 protons, and 16 neutrons

2an oxygen atom with 4 electrons, 6 protons, and 4 neutrons

3an oxygen atom with 9 electrons, 8 protons, and 8 neutron

4an oxygen atom with 8 electrons, 8 protons, and 9 neutrons

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.

Use a magnet to separate iron, evaporate water, i'm not sure how to separate the other two i'm sorry but good luck