Which of the following is fool's gold?

Options

A. `CuFeS_2`
B. `Cu(OH)_2`
C. `Cu(OH)_2.CuCO_3`
D. `Cu_2S`

Explanation

To determine which of the following compounds is known as fool's gold, we will analyze each option provided:

1. **Cu2S (Copper Sulfide)**: This compound is known as chalcocite. It is not referred to as fool's gold.

2. **CuOH2 (Copper Hydroxide)**: This compound is a hydroxide of copper and is not associated with fool's gold. It is often used as a fungicide or in other applications.

3. **CuOH2.CuCO3 (Basic Copper Carbonate)**: This compound is a combination of copper hydroxide and copper carbonate. It is mainly used as a pigment and does not relate to fool's gold.

4. **CuFeS2 (Copper Iron Sulfide)**: This compound is known as chalcopyrite. It is also associated with pyrite (FeS2), which is commonly referred to as fool's gold due to its metallic luster and pale golden hue, resembling that of gold.

From the analysis, the correct answer is:

**CuFeS2 (Chalcopyrite)** is known as fool's gold.

### Steps Summary:
1. Analyze each compound option.
2. Identify the characteristics and common names of each compound.
3. Conclude that CuFeS2 is associated with fool's gold.