Ageologist finds an old rock and wants to determine its age using rubidium-strontium dating. this is possible because 87rb, which has a half-life of 4.75×1010 y, undergoes β − decay and becomes 87sr. the geologist determines that the ratio of 87sr to 87rb is 0.183. assuming there was no 87sr in the rock when it was formed, determine the age of the rock.

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.