Final answer:
Table salt is a pure substance because it is a compound with a uniform and definite composition. Bronze is a homogeneous mixture, air is a homogeneous mixture of gases, and soil is a heterogeneous mixture. Therefore, the only pure substance listed is table salt.
Step-by-step explanation:
The question asks which of the following is a pure substance: a. table salt, b. bronze, c. air, d. soil. Pure substances are categorized into two classes: elements and compounds. They have uniform and definite compositions and cannot be separated into simpler substances by physical means. Here's how the mentioned substances classify:
- Table salt (sodium chloride) is a compound and therefore a pure substance.
- Bronze is an alloy, which is a homogeneous mixture of two or more elements, typically metals.
- Air is a homogeneous mixture of various gases, primarily nitrogen and oxygen.
- Soil is a heterogeneous mixture containing organic matter, minerals, gases, liquids, and countless organisms.
Therefore, the answer to the student's question is a. table salt.