Which amongst the following is not free state of carbon?

Options

A. Diamond
B. Graphite
C. Coke
D. Petroleum

Answer

To determine which option is not a free state of carbon, let's analyze each option provided:

1. **Diamond**:
- Diamond is one of the allotropes of carbon. It is a crystalline form where each carbon atom is bonded to four other carbon atoms in a tetrahedral structure. Therefore, diamond is a free state of carbon.

2. **Graphite**:
- Graphite is another allotrope of carbon. In graphite, carbon atoms are arranged in layers, with each carbon atom bonded to three others in a planar structure. This structure allows layers to slide over each other, making graphite a good lubricant. Thus, graphite is also a free state of carbon.

3. **Coke**:
- Coke is a form of carbon obtained from the destructive distillation of coal. It is primarily composed of carbon and is used as a fuel and reducing agent in metallurgical processes. Therefore, coke is also considered a free state of carbon.

4. **Petroleum**:
- Petroleum is a complex mixture of hydrocarbons and other organic compounds formed from the remains of ancient plants and animals buried under layers of sediment. It is classified as a fossil fuel and does not exist in a pure form of carbon. Hence, petroleum is not a free state of carbon.

Based on this analysis, the answer to the question "Which amongst the following is not a free state of carbon?" is **D. Petroleum**.

### Step-by-Step Solution:
1. Identify the options: Diamond, Graphite, Coke, Petroleum.
2. Define what a free state of carbon is: Allotropes or forms of carbon that exist independently.
3. Analyze each option:
- Diamond: Allotrope of carbon, free state.
- Graphite: Allotrope of carbon, free state.
- Coke: Form of carbon from coal, free state.
- Petroleum: Fossil fuel, not a pure form of carbon.
4. Conclude that Petroleum is not a free state of carbon.