The solution among the given options is Pure gold.
Here's why:
1. **Oil in water**: This is a mixture where oil and water do not combine to form a single phase. It's not a solution because the components remain separate.
2. **Sand in water**: Similar to the oil-water mixture, sand and water do not form a homogeneous solution; they are visibly distinct from each other.
3. **Soil**: Soil is a heterogeneous mixture consisting of various substances like minerals, organic matter, air, and water. It's not a solution because the components are not uniformly distributed.
4. **Pure gold**: Pure gold is a metal composed solely of gold atoms. When gold is not mixed or alloyed with other metals, it forms a homogeneous solution of gold atoms. In this case, pure gold qualifies as a solution due to its uniform composition.
5. **Steel**: Steel is an alloy composed of iron and carbon, often with other elements. It is not a solution in the traditional sense because it is a mixture of different elements, not a single substance like pure gold.
