Discuss whether each of the following is a mixture or a pure substance. If it is a mixture, please state if it homogeneous or heterogeneous. Please give your reasoning for each case. If it is difficult to tell, explain why.
1. Seawater.
2. Chocolate.
3. Table sugar.
4. An apple.
5. A sheet of paper
6. The spice paprika.
7. Seven Up.