What is the oxidation number of nitrogen in hno2?

+1
-1
+3
-3

The correct answer is +3

That is because the number of the entire molecule must always be 0. Since O2 equals -4 because individual oxygen atoms are -2, and Hydrogen (H) is +1, then you can see that H +1, + 3 from N, -4 from O2 = 0.

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.