Explain why the layer of petroleum is above the water.

Explanation

### Step-by-Step Solution:

1. **Understanding the Concept of Density**:
- Density is defined as the mass of a substance per unit volume. It is a key property that determines whether a substance will float or sink in another substance.

2. **Comparing Densities of Water and Petroleum**:
- Water has a density of approximately 1 g/cm³. In contrast, petroleum (or oil) has a lower density, typically around 0.8 g/cm³. This means that petroleum is lighter than water.

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