3. It is a mixture. 14-karat gold is an alloy of gold and other metals such as copper and silver. Pure gold is referred to as 24-karat gold. For example, Propane is a chemical substance so it is a pure substance.
4. Basically, atoms and elements are the same thing. Atoms are the smallest components of matter, consisting of a nucleus containing combinations of neutrons and protons. The element, Hydrogen, is made from atoms containing just one proton and one electron.