Answer:
The subscript next to the letter "C" will always tell you the number of carbon atoms.
Streak. It couldn't be hardness because some minerals are soft and metallic, and some are hard and metallic. Also, it can't be luster, because most gems are minerals, and most luster, but they're not metallic. And it can't be magnetism, because magnetite, the only magnetic mineral, is not really metallic.
Answer:
This is because it is a physical change not a chemical change.