In the Middle Ages, most scientists believed that the world was made from four simple elements
and that almost everything was a mixture.
Which type of pure substance had they not
yet discovered?

The world made up of four elements according to my understanding which is fire,water,earth and air but copper is also part of the simple elements so the answer is copper

Since there is the same amount of agn03 in both silver chloride and silver nitrate they produce the same amount of moles. therefore silver chloride produces the same amount of silver nitrate, so your answer is 15.0 moles of silver nitrate. i hope this !