If, in the previous question, there is a 15 N kinetic frictional force opposing the motion, how much work is
done by the force of friction? Does friction do positive
work or negative work on the block? Draw a free-body
diagram to support your answer.

The answer is a) carbon-12

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.

The answer is nitrogen-containing bases

Hi + naoh -> h2o + nal