A student places 2 mL of 2% ethanolic silver nitrate solution into test tube. They add 2 drops of an unknown compound into the test tube while gently mixing. After five minutes, the student heated the test tube in a water bath and a white precipitate formed. They added 2 drops of 1 M nitric acid to the mixture which was cooled to room temperature and still noticed the precipitate did not dissolve in response to the nitric acid. What compound is most likely the unknown