In which main energy level does the 's' sublevel first appear? k (first main energy level) l (second main energy level) m (third main energy level) n (fourth main energy level)

1. B, because in the 1s you don't have a p orbital, only in 2p, so the second level. 

Sorry i dont understand the question can you rephase it?

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.