In which of the substances in figure 3-1 are the forces of attraction among the particles so weak that they can be ignored under ordinary conditions?
a. substance a
b. substance b
c. substance c
d. substance a, b, and c

Substance C can be compared with gaseous particles in which intermolecular forces are so weak because particles are far from each other. 
Hence option C is correct.

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.