title: Salt (chemistry)
context: Solid salts tend to be transparent as illustrated by sodium chloride. In many cases, the apparent opacity or transparency are only related to the difference in size of the individual monocrystals. Since light reflects from the grain boundaries (boundaries between crystallites), larger crystals tend to be transparent, while the polycrystalline aggregates look like white powders.
question: What's the chemical compound of salt?
answers: sodium chloride