Select the property which forms the basis of hydrometallurgical process that is used for extraction of gold.

Options

A. Gold is electropositive metal
B. Gold is less reactive metal
C. Gold forms complexes that are water soluble.
D. Gold forms salts, which are water soluble.

Explanation

To solve the question regarding the property that forms the basis of the hydrometallurgical process used for the extraction of gold, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Hydrometallurgy**:
- Hydrometallurgy is a method used to extract metals from their ores using aqueous solutions. This process is particularly useful for metals like gold, which can be extracted from low-grade ores.

2. **Identifying the Properties of Gold**:
- We need to analyze the properties of gold provided in the options:
- Gold is an electropositive metal.
- Gold is a less reactive metal.
- Gold forms complexes that are water-soluble.
- Gold forms salts that are water-soluble.

3. **Analyzing Each Property**:
- **Electropositive Metal**: While gold is electropositive, this property does not specifically relate to its extraction via hydrometallurgy.
- **Less Reactive Metal**: Gold’s low reactivity is a characteristic but does not directly explain the hydrometallurgical extraction process.
- **Forms Complexes that are Water-Soluble**: This is a crucial property. Gold can react with cyanide in the presence of oxygen and water to form a soluble complex, which can be easily extracted from the solution.
- **Forms Salts that are Water-Soluble**: This is somewhat related but less specific than the complex formation.

4. **Conclusion**:
- The property that forms the basis of the hydrometallurgical process used for the extraction of gold is that **gold forms complexes that are water-soluble**. This allows gold to be effectively leached from its ore using cyanide solutions.

### Final Answer:
Gold forms complexes that are water-soluble.